code: public function getParent($id)
      {
          $node = $this->getSelf($id);
          if ($node) {
              $parentId = $node->{$this->getTreeNodeParentIdName()};
  
              return $this->getSelf($parentId);
          }
      }
docs: 获取父一级节点.
  
  @param mixed $id
  
  @return mixed