在Magento Connect里面安装EM Catalog Menu Widget Extension Key: 

magento-community/EM_CatalogMenuWidget

static block用法 

<div class="leftmenu">
	<h2>Main Products Category</h2>
	{{widget type="catalogmenuwidget/catalogmenu" category="3" ul_class="level0" level_class="1" ul_id="my_nav" template="em_catalogmenuwidget/menu.phtml"}}
</div>

xml用法，这边调用的是static block 

<reference name="left">
	<block type="cms/block" name="workbenchesmenu" before="-">
		<action method="setBlockId"><block_id>workbenchesmenu</block_id></action>
	</block>
</reference>