public function getSubTree(\ORC\Util\Tree\INode $node)
 {
     $tree = new self($node);
     $childrenKeys = $this->getAllChildrenKeys($node->getKey());
     foreach ($childrenKeys as $key) {
         $child = $this->get($key);
         $tree->addByKey($child, $this->parentKeys[$key]);
     }
     return $tree;
 }