[flexcoders] Tree View Issue

[lehaianh1986]

I use mx:Tree to view my data in XMLList. I want to show Tree in default with 
expand all item. I use method tree.expandItem() but it does not run.
Here is my code

<mx:WindowedApplication xmlns:mx="http://www.adobe.com/2006/mxml";
        layout="vertical"
        applicationComplete="init()">
<mx:Script>
        <![CDATA[
           private function init():void{
                 callLater(showtree);
           }
           private function showtree():void{
                 tree.expandItem(treeData, true, true);
           }
        ]]>
</mx:Script>
<mx:XMLList id="treeData">  
                <node label="One">
                   <node label="1.1" />
                   <node label="1.2" />
                   <node label="1.3" />
                   <node label="1.4"/>
                   <node label="1.5"/>
                </node>                 
                <node label="Two">            
                   <node label="2.1"/>
                   <node label="2.2"/>
                </node>
</mx:XMLList>
<mx:Tree id="tree"
            dataProvider="{treeData}"
            showRoot="false"
            labelField="@label"
            width="300"/>
  
</mx:WindowedApplication>

Anyone can show me where is false?