code: def ontologyPropTree(self):
          
          treedict = {}
          if self.all_properties:
              treedict[0] = self.toplayer_properties
              for element in self.all_properties:
                  if element.children():
                      treedict[element] = element.children()
              return treedict
          return treedict
docs: Returns a dict representing the ontology tree
          Top level = {0:[top properties]}
          Multi inheritance is represented explicitly