http://www.zkoss.org/forum/listComment/17743

test case
—
<hlayout width="100%">
<tree id="tree" width="400px" rows="8" multiple="true" onSelect='_selection.setValue( "Selected items: " + event.getSelectedItems() );'>
<treecols sizable="true">
<treecol label="Name" />
<treecol label="Description" />
</treecols>
<treechildren>
<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>
<treeitem>
<treerow>
<treecell label="Item 2.1.2" />
</treerow>
</treeitem>
</treechildren>
</treeitem>
<treeitem>
<treerow>
<treecell label="Item 2.2" />
</treerow>
<treechildren>
<treeitem>
<treerow>
<treecell label="Item 2.2.1" />
</treerow>
</treeitem>
</treechildren>
</treeitem>
</treechildren>
</treeitem>
<treeitem label="Item 3" />
</treechildren>
</tree>
<label id="_selection" />
</hlayout>