在Ext.Ajax.request成功请求的success的函数里对外部的panel添加item

var privilege = new Ext.Panel( {
id:"sss",
region:"west",
layout:"accordion",
collapsible:true,
width:250,
layoutConfig:{
titleCollapse:true,
animate:true,
activeOnTop:false
}
});

Ext.Ajax.request( {
url : "ajax/privilege!loadPrivilegeAccordion.action",
success : function(response) {
var json = Ext.decode(response.responseText);
var accordion = json.privilegeAccordion;
for(var i=0;i<accordion.length;i++) {

var titleStr = accordion[i].title;
var idStr = accordion[i].id;
alert(titleStr);
alert(idStr);
var item = new Ext.Panel({
         title:"s",items:[
         new Ext.tree.TreePanel({
                 rootVisible: false,
                 loader:new Ext.tree.TreeLoader({
                 processResponse:treeLoaderProcessResponse,
                 dataUrl:"ajax/privilege!loadPrivilegeTreeNode.action"
}),
root:new Ext.tree.AsyncTreeNode({
id:"1",expanded:true,text:"s"
})
         })]
});
privilege.add(item);//像这样添加添加不进去啊,也不报错,这里应该如何添加啊?
}
},
failure: function(response) {
alert(response.responseText);
  }
});