Problem in retreiving label of child node

<?page title="new page title" contentType="text/html;charset=UTF-8"?>
<?init class="org.zkoss.zkplus.databind.AnnotateDataBinderInit" ?>
<zk>
<window title="new page title" border="normal">


<tree id="tree" width="400px" rows="8" onSelect="onSelect_trMenu()">
	<treecols sizable="true">
		<treecol label="Name" />
		<treecol label="Description" />
	</treecols>
	<treechildren id="trMenu">
		<treeitem>
			<treerow>
				<treecell label="Item 1" />
				<treecell label="Item 1 description" />
			</treerow>
		</treeitem>
		<treeitem>
			<treerow>
				<treecell label="Item 2" />
				<treecell label="Item 2 description" />
			</treerow>
			<treechildren>
				<treeitem>
					<treerow>
						<treecell label="Item 2.1" />
					</treerow>
					<treechildren>
						<treeitem>
							<treerow>
								<treecell label="Item 2.1.1" />
							</treerow>
						</treeitem>
...
...
...
...
</tree>
<zscript>
	<![CDATA[ 

	void onSelect_trMenu()
	{
    	Tree TR= trMenu.getTree();
    	Treeitem ITS = tree.getSelectedItem();
    	alert(ITS.getLabel()+" level of tree:"+ITS.getLevel());
	}
	]]>
</zscript>
</window>
</zk>