private function insertChunk($fileId, $data, $chunkNumber)
    {
        $chunk = [
            'files_id' => $fileId,
            'n' => $chunkNumber,
            'data' => new MongoBinData($data),
        ];

        $result = $this->chunks->insert($chunk);

        if (! $this->isOKResult($result)) {
            throw new \MongoException('error inserting chunk');
        }

        return $result;
    }