insertArr = [
  [
    '_id'   => new \MongoDB\BSON\ObjectId(),
    'name'  => 'teste
  ]
];

$collection = $this->mongo->webapp->hosting;
$collection->updateOne(
    ['_id' =>new \MongoDB\BSON\ObjectId($hostingId), 'rooms._id' => new \MongoDB\BSON\ObjectId($roomId)],
    ['$push' => ['rooms.$.media' => ['$each' => $insertArr ]]]
);