Sets the grouping information for this tree.
        
        :param      groupBy | [<str> group level, ..] || None

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