The source code

    /*!
     * Ext JS Library 3.2.1
     * Copyright(c) 2006-2010 Ext JS, Inc.
     * licensing@extjs.com
     * http://www.extjs.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 = 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("beforechildrenrendered", this.doSort, this);
        tree.on("append", this.updateSort, this);
        tree.on("insert", this.updateSort, this);
        tree.on("textchange", this.updateSortParent, this);

        var dsc = this.dir && this.dir.toLowerCase() == "desc";
        var p = this.property || "text";
        var sortType = this.sortType;
        var fs = this.folderSort;
        var cs = this.caseSensitive === true;
        var leafAttr = this.leafAttr || 'leaf';

        this.sortFn = function(n1, n2){
            if(fs){
                if(n1.attributes[leafAttr] && !n2.attributes[leafAttr]){
                    return 1;
                }
                if(!n1.attributes[leafAttr] && n2.attributes[leafAttr]){
                    return -1;
                }
            }
            var v1 = sortType ? sortType(n1) : (cs ? n1.attributes[p] : n1.attributes[p].toUpperCase());
            var v2 = sortType ? sortType(n2) : (cs ? n2.attributes[p] : n2.attributes[p].toUpperCase());
            if(v1 < v2){
                return dsc ? +1 : -1;
            }else if(v1 > v2){
                return dsc ? -1 : +1;
            }else{
                return 0;
            }
        };
    };

    Ext.tree.TreeSorter.prototype = {
        doSort : function(node){
            node.sort(this.sortFn);
        },

        compareNodes : function(n1, n2){
            return (n1.text.toUpperCase() > n2.text.toUpperCase() ? 1 : -1);
        },

        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]);
            }
        }
    };