def ontologyClassTree(self):
        """
        Returns a dict representing the ontology tree
        Top level = {0:[top classes]}
        Multi inheritance is represented explicitly
        """
        treedict = {}
        if self.all_classes:
            treedict[0] = self.toplayer_classes
            for element in self.all_classes:
                if element.children():
                    treedict[element] = element.children()
            return treedict
        return treedict