Filtering elements of a tree

Hi all,
I am having an xml like this -

<Topic id="5" Text="music">
	<category id="6" Text="blues">
		<artist id="7" Text="bb king"/>
		<artist id="8" Text="lightnin hopkins"/>
	</category>
	<category id="6" Text="red">
		<Category id="11" Text="bb">
			<artist id="8" Text="lightnin hopkins"/>
		</Category>
	</category>
	<category id="6" Text="jazz">
		<category id="11" Text="bebop">
			<artist id="7" Text="charlie parker"/>
		</category>
		<artist id="7" Text="miles davis"/>
		<artist id="10" Text="john coltrane"/>
	</category>
</Topic>

<TreeNode id="5" Text="music">
	<TreeNode id="6" Text="blues">
		<TreeNode id="7" Text="bb king"/>
	</TreeNode>
	<TreeNode id="6" Text="jazz">
		<TreeNode id="11" Text="bebop">
			<TreeNode id="7" Text="charlie parker"/>
		</TreeNode>
		<TreeNode id="7" Text="miles davis"/>
	</TreeNode>
</TreeNode>