TreeManager.addManager

Adds a sub manager to manager. Use this method to create the skeleton structure of a #GdaTree. Note that a single #GdaTreeManager can be used by several #GdaTree objects or several times in the same #GdaTree's structure.

Please note that it's possible for mgr and sub to be the same object, but beware of the possible infinite recursive behaviour in this case when creating children nodes (depending on the actual implementation of the #GdaTreeManager).