XSLT - adding tag to a flat document structure

[D Tom <xml4u2002@yahoo.com>]

Hi

I need to maintain the hierarchical grouping method
using XSLT.

How to convert the following input to hirearchical
output using XLST.

Please Advice.

Input:
========

<Main>main</Main>
<Sub1>sub1</Sub1>
<Sub2>sub 2</Sub2>
<Sub2>sub 2</Sub2>  
<Sub1>sub 1</Sub1>
<Sub2>sub 2</Sub2>
<Sub2>sub 2</Sub2>

Output
========

<Main>main
   <Sub1>sub1
        <Sub2>sub 2</Sub2>
        <Sub2>sub 2</Sub2>
   </Sub1>
   <Sub1>sub 1
       <Sub2>sub 2</Sub2>
       <Sub2>sub 2</Sub2>
   </Sub1>
</Main>

Regards
Tom

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