creating nesting from flat xml

thank you in advance.
darrell dupas

=====================
<xmlfile type="before-transform" >
<a>grp1 title</a>
<b>grp1 member a </b>
<b>grp1 member b </b>
<a>grp2 title</a>
<b>grp2 member a </b>
<b>grp2 member b </b>
<b>grp2 member c </b>
<b>grp2 member d </b>
<a>grp3 title </a>
<b>grp3 member a</b>
</xmlfile>
=========================
<xmlfile type="desired-result" >
<div>
 <a>grp1 title</a>
 <b>grp1 member a </b>
 <b>grp1 member b </b>
</div>
<div>
 <a>grp2 title</a>
 <b>grp2 member a </b>
 <b>grp2 member b </b>
 <b>grp2 member c </b>
 <b>grp2 member d </b>
</div>
<div>
 <a>grp3 title </a>
 <b>grp3 member a</b>
</div>
</xmlfile>