code: private static <T extends HierarchyEntity<T, ?>> void loadChildren(T node, Set<T> children) {
      if (null == node.getChildren()) { return; }
      for (T one : node.getChildren()) {
        children.add(one);
        loadChildren(one, children);
      }
    }
docs: 加载字节点
  
  @param node
  @param children