Fix nested groups

[ramya-rao-a]

This PR is to fix the parsing of nested groups.

Issue: When parsing nested groups, the inner group gets the outer most node as a parent

Eg: (div>dl>(dt+dd)*2) eventually gets expanded to

    <div>
       <dl></dl>
   </div>
   <dt></dt>
   <dd></dd>
   <dt></dt>
   <dd></dd>

instead of

    <div>
       <dl>
          <dt></dt>
          <dd></dd>
          <dt></dt>
         <dd></dd>
       </dl>
   </div>

cc @sergeche

[sergeche]

Published as v0.6.3