Extjs TreeGrid加载数据报未组织好

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.
 * [email protected]
 * 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 ' + Math.round(min * 60) + 'm';
                    } else {
                        return v + ' hour' + (v === 1 ? '' : 's');
                    }
                }
            }),
   editor: new Ext.form.NumberField({
                allowBlank: false,
                allowDecimals: true
            })
        },{
            header: 'Assigned To',
            width: 150,
            dataIndex: 'user',
   editor: new Ext.form.TextField({
                allowBlank: false
            })
        },{
   header: '操作',
            width: 130,
            buttons: ['update', 'remove'],
            buttonText: ['编辑', '删除']
  }],

        //dataUrl: 'treegrid-data.json'
  requestApi: {
            update: 'treegrid-data.json',
            remove: 'treegrid-data.json'
        }
       
    });
 
 var root = new Ext.tree.TreeNode({
        text: '根节点',
        expanded: true
    });
 tree.setRootNode(root);
 
  var nodes = {};
  nodes.children = mydata;/*TreeGrid的json数据[{……},{……}]*/
 function appendChild(node, o){
  if (o.children != null && o.children.length > 0) {
   for (var a = 0; a < o.children.length; a++) {
    var n = new Ext.tree.TreeNode({
     task:o.children[a].task,
     duration:o.children[a].duration,
     user:o.children[a].user,
     iconCls:o.children[a].iconCls
    });
    node.appendChild(n);
    appendChild(n, o.children[a]);
   }
  }
 }
 appendChild(root, nodes);
 
 new Ext.ButtonGroup({
        renderTo: Ext.getBody(),
        title: 'States',
        style: 'padding:20px 50px;',
        columns: 2,
        items: [{
            text: 'Hidden',
            width: 100,
            handler: function() {
                tree.hideButton('node-1', 'update');
            }
        }, {
            text: 'Show',
            width: 100,
            handler: function() {
                tree.showButton('node-1', 'update');
            }
        }]
    });
 
});