code: def update_all_nodes(self):
          
          item_model_controller = self.item_model_controller
          if item_model_controller:
              if self.__node_counts_dirty:
                  for item in self.__mapping.values():
                      if "tree_node" in item.data:  # don't update the root node
                          tree_node = item.data["tree_node"]
                          item.data["display"] = self.__display_for_tree_node(tree_node)
                          item_model_controller.data_changed(item.row, item.parent.row, item.parent.id)
                  self.__node_counts_dirty = False
docs: Update all tree item displays if needed. Usually for count updates.