[xsl] transforming siblings to a hierarchy

["John Smith" <debrief@xxxxxxxxx>]

Hello,

How can change the following:

<a/>
<plus/>
<b/>
<minus/>
<c/>
<plus/>
<d/>
<plus/>
<e/>

To the following:


<addition>
    <addition>
        <takeaway>
            <addition>
                <a/>
                <b/>
           </addition>
           </c>
        </takeaway>
        <d/>
    </addition>
</addition>

Many thanks,
John