extjs 树

var treeNodes = {
text:'根',
expand:true,
children:[
{text:'叶子1',leaf:true},
{text:'叶子2',leaf:true},
]
};
var treePanel = new Ext.tree.TreePanel({
title:'This is tree test',
width: 200,
height: 150,
root:treeNodes,
autoScroll:true,
renderTo: Ext.getBody()
});
倒腾了一上午，这么简单的一个东西还没出来。。求解，，，，