diff --git a/blocks/navigation/renderer.php b/blocks/navigation/renderer.php
index 3c8932c306b..131c559ec4a 100644
--- a/blocks/navigation/renderer.php
+++ b/blocks/navigation/renderer.php
@@ -140,7 +140,8 @@ class block_navigation_renderer extends plugin_renderer_base {
                 $liclasses[] = 'contains_branch';
                 if ($depth == 1) {
                     $liexpandable = array(
-                        'data-expandable' => 'false'
+                        'data-expandable' => 'false',
+                        'data-collapsible' => 'false'
                     );
                 } else {
                     $liexpandable = array(
diff --git a/lib/amd/build/tree.min.js b/lib/amd/build/tree.min.js
index abc9f1d60b6..f29cc28ee04 100644
--- a/lib/amd/build/tree.min.js
+++ b/lib/amd/build/tree.min.js
@@ -1 +1 @@
-define(["jquery"],function(a){var b={ITEM:"[role=treeitem]",GROUP:"[role=treeitem]:has([role=group]), [role=treeitem][data-requires-ajax=true]",CLOSED_GROUP:"[role=treeitem]:has([role=group])[aria-expanded=false], [role=treeitem][data-requires-ajax=true][aria-expanded=false]",FIRST_ITEM:"[role=treeitem]:first",VISIBLE_ITEM:"[role=treeitem]:visible",UNLOADED_AJAX_ITEM:"[role=treeitem][data-requires-ajax=true][data-loaded=false][aria-expanded=true]"},c=function(c,d){this.treeRoot=a(c),this.treeRoot.data("activeItem",null),this.selectCallback=d,this.keys={tab:9,enter:13,space:32,pageup:33,pagedown:34,end:35,home:36,left:37,up:38,right:39,down:40,asterisk:106},this.initialiseNodes(this.treeRoot),this.setActiveItem(this.treeRoot.find(b.FIRST_ITEM)),this.refreshVisibleItemsCache(),this.bindEventHandlers()};return c.prototype.refreshVisibleItemsCache=function(){this.treeRoot.data("visibleItems",this.treeRoot.find(b.VISIBLE_ITEM))},c.prototype.getVisibleItems=function(){return this.treeRoot.data("visibleItems")},c.prototype.setActiveItem=function(a){var b=this.treeRoot.data("activeItem");a!==b&&(null!==b&&(b.attr("tabindex","-1"),b.attr("aria-selected","false")),a.attr("tabindex","0"),a.attr("aria-selected","true"),this.treeRoot.data("activeItem",a),"function"==typeof this.selectCallback&&this.selectCallback(a))},c.prototype.isGroupItem=function(a){return a.is(b.GROUP)},c.prototype.initialiseNodes=function(c){this.removeAllFromTabOrder(c),this.setAriaSelectedFalseOnItems(c);var d=this;c.find(b.UNLOADED_AJAX_ITEM).each(function(){var b=a(this);d.collapseGroup(b),d.expandGroup(b)})},c.prototype.removeAllFromTabOrder=function(a){a.find("*").attr("tabindex","-1")},c.prototype.setAriaSelectedFalseOnItems=function(a){a.find(b.ITEM).attr("aria-selected","false")},c.prototype.expandAllGroups=function(){this.expandAllChildGroups(this.treeRoot)},c.prototype.expandAllChildGroups=function(c){var d=this;c.find(b.CLOSED_GROUP).each(function(){var b=a(this);d.expandGroup(b).done(function(){d.expandAllChildGroups(b)})})},c.prototype.expandGroup=function(b){var c=a.Deferred();if("false"!==b.attr("data-expandable")&&"true"!==b.attr("aria-expanded"))if("true"===b.attr("data-requires-ajax")&&"true"!==b.attr("data-loaded")){b.attr("data-loaded",!1);var d=b.closest("[data-ajax-loader]").attr("data-ajax-loader"),e=this;b.addClass("loading"),require([d],function(a){a.load(b).done(function(){b.attr("data-loaded",!0),e.initialiseNodes(b),e.finishExpandingGroup(b),b.removeClass("loading"),c.resolve()})})}else this.finishExpandingGroup(b),c.resolve();else c.resolve();return c},c.prototype.finishExpandingGroup=function(a){var c=a.children(b.GROUP);c.show().attr("aria-hidden","false"),a.attr("aria-expanded","true"),this.refreshVisibleItemsCache()},c.prototype.collapseGroup=function(a){if("false"!==a.attr("aria-expanded")){var c=a.children(b.GROUP);c.hide().attr("aria-hidden","true"),a.attr("aria-expanded","false"),this.refreshVisibleItemsCache()}},c.prototype.toggleGroup=function(a){"true"===a.attr("aria-expanded")?this.collapseGroup(a):this.expandGroup(a)},c.prototype.handleKeyDown=function(a,c){var d=this.getVisibleItems().index(a);if(c.altKey||c.ctrlKey||c.shiftKey&&c.keyCode!=this.keys.tab)return!0;switch(c.keyCode){case this.keys.home:return this.getVisibleItems().first().focus(),c.stopPropagation(),!1;case this.keys.end:return this.getVisibleItems().last().focus(),c.stopPropagation(),!1;case this.keys.enter:var e=a.children().not(b.GROUP).children("a");return e.length?window.location.href=e.first().attr("href"):this.isGroupItem(a)&&this.toggleGroup(a,!0),c.stopPropagation(),!1;case this.keys.space:return this.isGroupItem(a)&&this.toggleGroup(a,!0),c.stopPropagation(),!1;case this.keys.left:if(this.isGroupItem(a)){this.collapseGroup(a);var f=this.getVisibleItems().filter(b.GROUP),g=f.index(a),h=g-1>0?g-1:0;f.eq(h).focus()}return c.stopPropagation(),!1;case this.keys.right:return this.isGroupItem(a)&&this.expandGroup(a).done(function(){a.find(b.ITEM).first().focus()}),c.stopPropagation(),!1;case this.keys.up:if(d>0){var i=this.getVisibleItems().eq(d-1);i.focus()}return c.stopPropagation(),!1;case this.keys.down:if(d<this.getVisibleItems().length-1){var j=this.getVisibleItems().eq(d+1);j.focus()}return c.stopPropagation(),!1;case this.keys.asterisk:return this.expandAllGroups(),c.stopPropagation(),!1}return!0},c.prototype.handleClick=function(a,b){return b.altKey||b.ctrlKey||b.shiftKey?!0:(a.focus(),this.isGroupItem(a)&&this.toggleGroup(a),b.stopPropagation(),!0)},c.prototype.handleFocus=function(a,b){return this.setActiveItem(a),b.stopPropagation(),!0},c.prototype.bindEventHandlers=function(){var c=this;this.treeRoot.on({click:function(b){return c.handleClick(a(this),b)},keydown:function(b){return c.handleKeyDown(a(this),b)},focus:function(b){return c.handleFocus(a(this),b)}},b.ITEM)},c});
\ No newline at end of file
+define(["jquery"],function(a){var b={ITEM:"[role=treeitem]",GROUP:"[role=treeitem]:has([role=group]), [role=treeitem][data-requires-ajax=true]",CLOSED_GROUP:"[role=treeitem]:has([role=group])[aria-expanded=false], [role=treeitem][data-requires-ajax=true][aria-expanded=false]",FIRST_ITEM:"[role=treeitem]:first",VISIBLE_ITEM:"[role=treeitem]:visible",UNLOADED_AJAX_ITEM:"[role=treeitem][data-requires-ajax=true][data-loaded=false][aria-expanded=true]"},c=function(c,d){this.treeRoot=a(c),this.treeRoot.data("activeItem",null),this.selectCallback=d,this.keys={tab:9,enter:13,space:32,pageup:33,pagedown:34,end:35,home:36,left:37,up:38,right:39,down:40,asterisk:106},this.initialiseNodes(this.treeRoot),this.setActiveItem(this.treeRoot.find(b.FIRST_ITEM)),this.refreshVisibleItemsCache(),this.bindEventHandlers()};return c.prototype.refreshVisibleItemsCache=function(){this.treeRoot.data("visibleItems",this.treeRoot.find(b.VISIBLE_ITEM))},c.prototype.getVisibleItems=function(){return this.treeRoot.data("visibleItems")},c.prototype.setActiveItem=function(a){var b=this.treeRoot.data("activeItem");a!==b&&(null!==b&&(b.attr("tabindex","-1"),b.attr("aria-selected","false")),a.attr("tabindex","0"),a.attr("aria-selected","true"),this.treeRoot.data("activeItem",a),"function"==typeof this.selectCallback&&this.selectCallback(a))},c.prototype.isGroupItem=function(a){return a.is(b.GROUP)},c.prototype.isGroupCollapsed=function(a){return"false"===a.attr("aria-expanded")},c.prototype.isGroupCollapsible=function(a){return"false"!==a.attr("data-collapsible")},c.prototype.initialiseNodes=function(c){this.removeAllFromTabOrder(c),this.setAriaSelectedFalseOnItems(c);var d=this;c.find(b.UNLOADED_AJAX_ITEM).each(function(){var b=a(this);d.collapseGroup(b),d.expandGroup(b)})},c.prototype.removeAllFromTabOrder=function(a){a.find("*").attr("tabindex","-1")},c.prototype.setAriaSelectedFalseOnItems=function(a){a.find(b.ITEM).attr("aria-selected","false")},c.prototype.expandAllGroups=function(){this.expandAllChildGroups(this.treeRoot)},c.prototype.expandAllChildGroups=function(c){var d=this;c.find(b.CLOSED_GROUP).each(function(){var b=a(this);d.expandGroup(b).done(function(){d.expandAllChildGroups(b)})})},c.prototype.expandGroup=function(b){var c=a.Deferred();if("false"!==b.attr("data-expandable")&&this.isGroupCollapsed(b))if("true"===b.attr("data-requires-ajax")&&"true"!==b.attr("data-loaded")){b.attr("data-loaded",!1);var d=b.closest("[data-ajax-loader]").attr("data-ajax-loader"),e=this;b.addClass("loading"),require([d],function(a){a.load(b).done(function(){b.attr("data-loaded",!0),e.initialiseNodes(b),e.finishExpandingGroup(b),b.removeClass("loading"),c.resolve()})})}else this.finishExpandingGroup(b),c.resolve();else c.resolve();return c},c.prototype.finishExpandingGroup=function(a){var c=a.children(b.GROUP);c.show().attr("aria-hidden","false"),a.attr("aria-expanded","true"),this.refreshVisibleItemsCache()},c.prototype.collapseGroup=function(a){if(this.isGroupCollapsible(a)&&!this.isGroupCollapsed(a)){var c=a.children(b.GROUP);c.hide().attr("aria-hidden","true"),a.attr("aria-expanded","false"),this.refreshVisibleItemsCache()}},c.prototype.toggleGroup=function(a){"true"===a.attr("aria-expanded")?this.collapseGroup(a):this.expandGroup(a)},c.prototype.handleKeyDown=function(a,c){var d=this.getVisibleItems().index(a);if(c.altKey||c.ctrlKey||c.shiftKey&&c.keyCode!=this.keys.tab)return!0;switch(c.keyCode){case this.keys.home:return this.getVisibleItems().first().focus(),c.stopPropagation(),!1;case this.keys.end:return this.getVisibleItems().last().focus(),c.stopPropagation(),!1;case this.keys.enter:var e=a.children().not(b.GROUP).children("a");return e.length?window.location.href=e.first().attr("href"):this.isGroupItem(a)&&this.toggleGroup(a,!0),c.stopPropagation(),!1;case this.keys.space:return this.isGroupItem(a)&&this.toggleGroup(a,!0),c.stopPropagation(),!1;case this.keys.left:var f=function(c){var d=c.getVisibleItems().filter(b.GROUP).has(a).last();d.focus()};return this.isGroupItem(a)?this.isGroupCollapsed(a)?f(this):this.collapseGroup(a):f(this),c.stopPropagation(),!1;case this.keys.right:return this.isGroupItem(a)&&(this.isGroupCollapsed(a)?this.expandGroup(a):a.find(b.ITEM).first().focus()),c.stopPropagation(),!1;case this.keys.up:if(d>0){var g=this.getVisibleItems().eq(d-1);g.focus()}return c.stopPropagation(),!1;case this.keys.down:if(d<this.getVisibleItems().length-1){var h=this.getVisibleItems().eq(d+1);h.focus()}return c.stopPropagation(),!1;case this.keys.asterisk:return this.expandAllGroups(),c.stopPropagation(),!1}return!0},c.prototype.handleClick=function(a,b){return b.altKey||b.ctrlKey||b.shiftKey?!0:(a.focus(),this.isGroupItem(a)&&this.toggleGroup(a),b.stopPropagation(),!0)},c.prototype.handleFocus=function(a,b){return this.setActiveItem(a),b.stopPropagation(),!0},c.prototype.bindEventHandlers=function(){var c=this;this.treeRoot.on({click:function(b){return c.handleClick(a(this),b)},keydown:function(b){return c.handleKeyDown(a(this),b)},focus:function(b){return c.handleFocus(a(this),b)}},b.ITEM)},c});
\ No newline at end of file
diff --git a/lib/amd/src/tree.js b/lib/amd/src/tree.js
index cb6d6ef269e..5b48d01a4c1 100644
--- a/lib/amd/src/tree.js
+++ b/lib/amd/src/tree.js
@@ -127,6 +127,28 @@ define(['jquery'], function($) {
         return item.is(SELECTORS.GROUP);
     };
 
+    /**
+     * Determines if the given group item (contains child tree items) is collapsed.
+     *
+     * @method isGroupCollapsed
+     * @param {object} item jquery object representing a group item on the tree.
+     * @returns {bool}
+     */
+    Tree.prototype.isGroupCollapsed = function(item) {
+        return item.attr('aria-expanded') === 'false';
+    };
+
+    /**
+     * Determines if the given group item (contains child tree items) can be collapsed.
+     *
+     * @method isGroupCollapsible
+     * @param {object} item jquery object representing a group item on the tree.
+     * @returns {bool}
+     */
+    Tree.prototype.isGroupCollapsible = function(item) {
+        return item.attr('data-collapsible') !== 'false';
+    };
+
     /**
      * Performs the tree initialisation for all child items from the given node,
      * such as removing everything from the tab order and setting aria selected
@@ -207,7 +229,7 @@ define(['jquery'], function($) {
     Tree.prototype.expandGroup = function(item) {
         var promise = $.Deferred();
         // Ignore nodes that are explicitly maked as not expandable or are already expanded.
-        if (item.attr('data-expandable') !== 'false' && item.attr('aria-expanded') !== 'true') {
+        if (item.attr('data-expandable') !== 'false' && this.isGroupCollapsed(item)) {
             // If this node requires ajax load and we haven't already loaded it.
             if (item.attr('data-requires-ajax') === 'true' && item.attr('data-loaded') !== 'true') {
                 item.attr('data-loaded', false);
@@ -266,8 +288,8 @@ define(['jquery'], function($) {
      * @param {Object} item is the jquery id of the parent item of the group.
      */
     Tree.prototype.collapseGroup = function(item) {
-        // If the item is already collapsed then do nothing.
-        if (item.attr('aria-expanded') === 'false') {
+        // If the item is not collapsible or already collapsed then do nothing.
+        if (!this.isGroupCollapsible(item) || this.isGroupCollapsed(item)) {
             return;
         }
 
@@ -344,15 +366,22 @@ define(['jquery'], function($) {
                 return false;
             }
             case this.keys.left: {
+                var focusParent = function(tree) {
+                    // Get the immediate visible parent group item that contains this element.
+                    var parentGroup = tree.getVisibleItems().filter(SELECTORS.GROUP).has(item).last();
+                    parentGroup.focus();
+                };
+
                 // If this is a goup item then collapse it and focus the parent group
                 // in accordance with the aria spec.
                 if (this.isGroupItem(item)) {
-                    this.collapseGroup(item);
-                    // Move up to the parent.
-                    var visibleGroups = this.getVisibleItems().filter(SELECTORS.GROUP);
-                    var index = visibleGroups.index(item);
-                    var prevIndex = (index - 1) > 0 ? index - 1 : 0;
-                    visibleGroups.eq(prevIndex).focus();
+                    if (this.isGroupCollapsed(item)) {
+                        focusParent(this);
+                    } else {
+                        this.collapseGroup(item);
+                    }
+                } else {
+                    focusParent(this);
                 }
 
                 e.stopPropagation();
@@ -362,10 +391,12 @@ define(['jquery'], function($) {
                 // If this is a group item then expand it and focus the first child item
                 // in accordance with the aria spec.
                 if (this.isGroupItem(item)) {
-                    this.expandGroup(item).done(function() {
+                    if (this.isGroupCollapsed(item)) {
+                        this.expandGroup(item);
+                    } else {
                         // Move to the first item in the child group.
                         item.find(SELECTORS.ITEM).first().focus();
-                    });
+                    }
                 }
 
                 e.stopPropagation();