docs: def setGroupBy(self, groupBy):
          """
          Sets the grouping information for this tree.
          
          :param      groupBy | [<str> group level, ..] || None
          """
          if groupBy and not type(groupBy) in (list, tuple):
              groupBy = [nativestring(groupBy)]
          elif not groupBy:
              groupBy = None
          
          self._groupBy = groupBy