xml to xml transform

Hi,

Given the folowing xml

<a>
  <b>1</b>
  <c>2</c>
  <d>
     <d1>text1</d1>
     <d2>text2</d2>
  </d>
<a>
<a>
  <b>1</b>
  <c>2</c>
  <d>
     <d1>more text1</d1>
     <d2>more text1</d2>
  </d>
<a>



how do I produce

<a>
  <b>1</b>
  <c>2</c>
  <d>
     <d1>text1</d1>
     <d2>text2</d2>
  </d>
  <d>
     <d1>more text1</d1>
     <d2>more text1</d2>
  </d>
<a>

I am not sure what this is called. is it grouping ?

thanks in advance.

Anu.