code: def _get_next_node(self, time_qualifier):
          
          hierarchy_entry = self.process_hierarchy.get_by_qualifier(time_qualifier)
          if hierarchy_entry.parent:
              parent_time_qualifier = hierarchy_entry.parent.process_entry.time_qualifier
              parent = self._get_next_node(parent_time_qualifier)
          else:
              parent = self.root
  
          return self._get_next_child_node(parent)
docs: Method goes to the top of the tree and traverses from
              there in search of the next suitable node for processing
              to the level defined by the given time_qualifier
              :param time_qualifier: defines target level of the tree
              :return: located node; type <TreeNode>