Add level classes to UL's

Thanks for great plugin.

I’m wondering is there simple way to add level class to ul tags. For example:

<ul class="page-list subpages-page-list level-1">
	<li class="page_item">list 1</li>
	<li class="page_item">list 1
		<ul class="children level-2">
			<li class="page_item">list 2</li>
			<li class="page_item">list 2</li>
				<ul class="children level-3">
					<li class="page_item">list 3</li>
					<li class="page_item">list 3</li>
					<li class="page_item">list 3</li>
						<ul class="children level-4">
							<li class="page_item">list 3</li>
							<li class="page_item">list 3</li>
							<li class="page_item">list 3</li>
						</ul>
					<li class="page_item">list 3</li>
					<li class="page_item">list 3</li>
				</ul>
			<li class="page_item">list 2</li>
		</ul>
	</li>
</ul>

http://ww.wp.xz.cn/extend/plugins/page-list/