[xsl] extracting and removing an element nested at different levels

["Mark" <mark@xxxxxxxxxxxx>]

I have XML consisting of <Item> elements that have nested <Item> elements at 
various depths within the tree, in its simplest form something like:

<List>
   <Item>
       <ElementA>
           <Item>
               <ElementB/>
           </Item>
       </ElementA>
   </Item>
</List>

That I want to render as:

<List>
   <Item>
       <ElementA/>
   </Item>
   <Item>
       <ElementB/>
   </Item>
</List>

Is there a general technique I can use to remove nested <Item> elements 
whatever their depth and place all <Item> elements at the same level within 
the <List>?
Thanks,
Mark