code: def _init_sub_groups(self, parent):
          
  
          if self._sub_groups:
              for sub_group in self._sub_groups:
                  for component in split_path_components(sub_group):
                      fp = os.path.join(parent.full_path, component)
                      if os.path.exists(fp):
                          node = Node(name=component, parent=parent)
                          parent.children.append(node)
                      else:
                          node = parent.create_cgroup(component)
                      parent = node
                  self._init_children(node)
          else:
              self._init_children(parent)
docs: Initialise sub-groups, and create any that do not already exist.