code: def ontologyClassTree(self):
          
          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
docs: Returns a dict representing the ontology tree
          Top level = {0:[top classes]}
          Multi inheritance is represented explicitly