想要实现 TreeGrid的效果，打开官方例子却看不到效果，怎么办呢？我是这样实现的

/*!
?* Ext JS Library 3.2.0
?* Copyright(c) 2006-2010 Ext JS, Inc.
?* licensing@extjs.com
?* http://www.extjs.com/license
?*/

Ext.onReady(function() {
??? Ext.QuickTips.init();
?
?var mydata = [
{
??? task:'Project: Shopping',duration:13.25,user:'Tommy Maintz',iconCls:'task-folder',expanded: true,
??? children:[
???? {task:'Housewares',duration:1.25,user:'Tommy Maintz',iconCls:'task-folder',
??children:[
???{task:'Kitchen supplies',duration:0.25,user:'Tommy Maintz',leaf:true,iconCls:'task'},
???{task:'Groceries',duration:.4,user:'Tommy Maintz',leaf:true,iconCls:'task'},
???{task:'Cleaning supplies',duration:.4,user:'Tommy Maintz',leaf:true,iconCls:'task'},
???{task: 'Office supplies',duration: .2,user: 'Tommy Maintz',leaf: true,iconCls: 'task'}
??]
???? },
???? {
??task:'Remodeling',duration:12,user:'Tommy Maintz',iconCls:'task-folder',expanded: true,
??children:[
???{task:'Retile kitchen',duration:6.5,user:'Tommy Maintz',leaf:true,iconCls:'task'},
???{task:'Paint bedroom',duration: 2.75,user:'Tommy Maintz',iconCls:'task-folder',
????children: [
??????{task: 'Ceiling',duration: 1.25,user: 'Tommy Maintz',iconCls: 'task',leaf: true},
??????{task: 'Walls',duration: 1.5,user: 'Tommy Maintz',iconCls: 'task',leaf: true}
?????? ]
???},
????????? {task:'Decorate living room',duration:2.75,user:'Tommy Maintz',leaf:true,iconCls:'task'},
????????? {task: 'Fix lights',duration: .75,user: 'Tommy Maintz',leaf: true,iconCls: 'task'},
????????? {task: 'Reattach screen door',duration: 2,user: 'Tommy Maintz',leaf: true,iconCls: 'task'}
???????? ]
???? }
??? ]
},
{? task:'Project: Testing',duration:2,user:'Core Team',iconCls:'task-folder',
?? children:[
??? {?task: 'Mac OSX',duration: 0.75,user: 'Tommy Maintz',iconCls: 'task-folder',
??children: [
???{task: 'FireFox',duration: 0.25,user: 'Tommy Maintz',iconCls: 'task',leaf: true},
???{task: 'Safari',duration: 0.25,user: 'Tommy Maintz',iconCls: 'task',leaf: true},
???{task: 'Chrome',duration: 0.25,user: 'Tommy Maintz',iconCls: 'task',leaf: true}
??]
?? },{?task: 'Windows',duration: 3.75,user: 'Darrell Meyer',iconCls: 'task-folder',
??children: [
???{task: 'FireFox',duration: 0.25,user: 'Darrell Meyer',iconCls: 'task',leaf: true},
???{task: 'Safari',duration: 0.25,user: 'Darrell Meyer',iconCls: 'task',leaf: true},
???{task: 'Chrome',duration: 0.25,user: 'Darrell Meyer',iconCls: 'task',leaf: true},
???{task: 'Internet Exploder',duration: 3,user: 'Darrell Meyer',iconCls: 'task',leaf: true}
??]
?? },{?task: 'Linux',duration: 0.5,user: 'Aaron Conran',iconCls: 'task',
??children: [
???{task: 'FireFox',duration: 0.25,user: 'Aaron Conran',iconCls: 'task',leaf: true},
???{task: 'Chrome',duration: 0.25,user: 'Aaron Conran',iconCls: 'task',leaf: true}
??]
?? }
?? ]
}
];
?
??? var tree = new Ext.ux.tree.TreeGrid({
??????? title: 'Core Team Projects',
??????? width: 700,
??????? height: 300,
??????? renderTo: Ext.getBody(),
??????? enableDD: true,

??????? columns:[{
??????????? header: 'Task',
??????????? dataIndex: 'task',
??????????? width: 230,
???editor: new Ext.form.TextField({
??????????????? allowBlank: false
??????????? })
??????? },{
??????????? header: 'Duration',
??????????? width: 100,
??????????? dataIndex: 'duration',
??????????? align: 'center',
??????????? sortType: 'asFloat',
??????????? tpl: new Ext.XTemplate('{duration:this.formatHours}', {
??????????????? formatHours: function(v) {
??????????????????? if(v < 1) {
??????????????????????? return Math.round(v * 60) + ' mins';
??????????????????? } else if (Math.floor(v) !== v) {
??????????????????????? var min = v - Math.floor(v);
??????????????????????? return Math.floor(v) + 'h '