[xsl] Another problem from Flat XML File to Hierarchical

["alex v." <alex.vett@xxxxxxxxx>]

I have a flat xml like this:

<level2></level2>
<level3></level3>
<level2></level2>
<level1></level1>
<level2></level2>
<level3></level3>
<level3></level3>

and I need to transform in a hierarchy structure like this using the
tag name as key:

<level2>
<level3></level3>
</level2>
<level2></level2>
<level1>
<level2>
<level3></level3>
<level3></level3>
</level2>
</level1>


Thanks in advance.

~av