Ext 的Tree型结构

动态树，当我选择一个节点并在该节点下增加节点，如何在该树控件reload后定位到当前选择的节点

代码如下

Ext.onReady(
function(){


var root = new Ext.tree.AsyncTreeNode(
{
text:"菜单根节点",
expanded:true,
id:'root'
});
var tree = new Ext.tree.TreePanel({
loader:new Ext.tree.TreeLoader({
baseAttrs:{
cust:'client'
},
dataUrl:'datatest.jsp'
}),
listeners : {
'click' : function(node, event) {
if (node.id == 'aa') {
getcount();
}

tree.getNodeById("aa").select();
},
'load':function(node, event) {
var a = tree.getNodeById("aa");
if (a!=null) {
a.select();
//alert('11111222654789');
}
}
},
title:'Tree示例',
width:200,
height:500,
autoHeight:true,

applyTo:'tree-div',
root:root

});
tree.on('load', function(node, event)
{
var a = tree.getNodeById("aa");
if (a!=null) {
a.select();
//alert('qqqqqqqqqqq');
}
});

});