How to merge XML files in a gradle script?

I'm converting a legacy project from an ANT build to Gradle, and I'm struggling to find a way to merge two XML files together.

File a:

<a>
   <attributes of a/>
</a>

File b:

<b>
   <attributes of b/>
</b>

Desired result:

<a>
   <attributes of a/>
</a>
<b>
   <attributes of b/>
</b>

Is there a good way to do this in a gradle task?