import mx.collections.ArrayCollection;
import mx.controls.List;
private function creationCompleteHandler(event:Event):void {
var array:Array = new Array({label: "CA", children: new Array(
{label: "Los Angeles"},
{label: "San Francisco"})},
{label: "MA", children: new Array(
{label: "Boston"})});
var collection:ArrayCollection = new ArrayCollection(array);
tree.dataProvider = collection;
}