public function getPrevSibling()
	{
		$right = $this->getLeftValue() - 1;
		if ($right <= 0) {
			return null;
		}
		$searchCondition = $this->repository->createSearchCondition()
				->rightEqualsTo($right);

		$prevSibling = $this->repository->search($searchCondition);
		if ( ! isset($prevSibling[0])) {
			return null;
		}
		$prevSibling = $prevSibling[0];
		
		return $prevSibling;
	}