 Extracts the value from a tree_node.</td></tr>
<tr><td valign="top"><a href="#group_children-5">group_children/5</a></td><td>
  Moves the children with PH ChildrenPHs to a new node, and
  puts the new node in the place of the children, it returns
  both the new node and the updated tree.</td></tr>
<tr><td valign="top"><a href="#index_by-2">index_by/2</a></td><td>
  Returns a map with the nodes of the Tree as values and the
  result of applying Fun to them as keys.</td></tr>
<tr><td valign="top"><a href="#i