The source code

    /*!
     * Ext JS Library 3.4.0
     * Copyright(c) 2006-2011 Sencha Inc.
     * licensing@sencha.com
     * http://www.sencha.com/license
     */
    /**
     * @class Ext.tree.TreeSorter
     * Provides sorting of nodes in a {@link Ext.tree.TreePanel}.  The TreeSorter automatically monitors events on the
     * associated TreePanel that might affect the tree's sort order (beforechildrenrendered, append, insert and textchange).
     * Example usage:

     *
    new Ext.tree.TreeSorter(myTree, {
        folderSort: true,
        dir: "desc",
        sortType: function(node) {
            // sort by a custom, typed attribute:
            return parseInt(node.id, 10);
        }
    });

     * @constructor
     * @param {TreePanel} tree
     * @param {Object} config
     */
    Ext.tree.TreeSorter = Ext.extend(Object, {

        constructor: function(tree, config){
            /**
         * @cfg {Boolean} folderSort True to sort leaf nodes under non-leaf nodes (defaults to false)
         */
        /**
         * @cfg {String} property The named attribute on the node to sort by (defaults to "text").  Note that this
         * property is only used if no {@link #sortType} function is specified, otherwise it is ignored.
         */
        /**
         * @cfg {String} dir The direction to sort ("asc" or "desc," case-insensitive, defaults to "asc")
         */
        /**
         * @cfg {String} leafAttr The attribute used to determine leaf nodes when {@link #folderSort} = true (defaults to "leaf")
         */
        /**
         * @cfg {Boolean} caseSensitive true for case-sensitive sort (defaults to false)
         */
        /**
         * @cfg {Function} sortType A custom "casting" function used to convert node values before sorting.  The function
         * will be called with a single parameter (the {@link Ext.tree.TreeNode} being evaluated) and is expected to return
         * the node's sort value cast to the specific data type required for sorting.  This could be used, for example, when
         * a node's text (or other attribute) should be sorted as a date or numeric value.  See the class description for
         * example usage.  Note that if a sortType is specified, any {@link #property} config will be ignored.
         */

        Ext.apply(this, config);
        tree.on({
            scope: this,
            beforechildrenrendered: this.doSort,
            append: this.updateSort,
            insert: this.updateSort,
            textchange: this.updateSortParent
        });

        var desc = this.dir && this.dir.toLowerCase() == 'desc',
            prop = this.property || 'text',
            sortType = this.sortType,
            folderSort = this.folderSort,
            caseSensitive = this.caseSensitive === true,
            leafAttr = this.leafAttr || 'leaf';

        if(Ext.isString(sortType)){
            sortType = Ext.data.SortTypes[sortType];
        }
        this.sortFn = function(n1, n2){
            var attr1 = n1.attributes,
                attr2 = n2.attributes;

            if(folderSort){
                if(attr1[leafAttr] && !attr2[leafAttr]){
                    return 1;
                }
                if(!attr1[leafAttr] && attr2[leafAttr]){
                    return -1;
                }
            }
            var prop1 = attr1[prop],
                prop2 = attr2[prop],
                v1 = sortType ? sortType(prop1) : (caseSensitive ? prop1 : prop1.toUpperCase()),
                v2 = sortType ? sortType(prop2) : (caseSensitive ? prop2 : prop2.toUpperCase());

            if(v1 < v2){
                return desc ? 1 : -1;
            }else if(v1 > v2){
                return desc ? -1 : 1;
            }
            return 0;
        };
        },

        doSort : function(node){
            node.sort(this.sortFn);
        },

        updateSort : function(tree, node){
            if(node.childrenRendered){
                this.doSort.defer(1, this, [node]);
            }
        },

        updateSortParent : function(node){
            var p = node.parentNode;
            if(p && p.childrenRendered){
                this.doSort.defer(1, this, [p]);
            }
        }
    });