Why flex tree not open in program?

Question

I have a simple flex tree, and I'd like to expand it after data load. but the tree is not expanding by expandChildrenOf method, expandItem, or openItems.

I could expand tree manually, though.

Here is the script:

private function resultHandler(event:ResultEvent):void
{
xmlTree = XML(event.result as String);
tree.dataProvider = xmlTree;
callLater(myExpandTree);
}

private function myExpandTree() : void {
    tree.expandChildrenOf(tree.root, true);
}

....

<mx:RemoteObject id="ro" destination="myList"
                 result="resultHandler(event)"
                 fault="faultHandler(event)"/>
<mx:XML id="xmlTree"/>

<mx:Tree id="tree" dataProvider="{xmlTree}"
         editable = "true"
         iconFunction="tree_iconFunc"

         labelField="@label"
         width="100%" height="100%" showRoot="false" />

Answer 1

This is what I used to expand the tree.

private function expandRootNode():void { tree.expandItem(xmlTree,true); //expand the root node }