private function findNodesWithoutParents()
    {
        // get nodes that have no parent but depth > 0
        $qb = $this->accountRepository->createQueryBuilder('c2')
            ->select('count(c2.id)')
            ->leftJoin('c2.parent', 'c1')
            ->where('c2.depth <> 0 AND c2.parent IS NULL');

        return $qb->getQuery()->getSingleScalarResult();
    }