<?php
require_once 'vendor/autoload.php';
$client = new MongoDB\Client;
$session = $client->startSession();
$session->startTransaction([
'readConcern' => new MongoDB\Driver\ReadConcern('snapshot'),
'writeConcern' => new MongoDB\Driver\WriteConcern('majority'),
]);
$client->test->foo->insertOne(['x' => 1], ['session' => $session]);
$client->test->bar->insertOne(['y' => 2], ['session' => $session]);
$session->commitTransaction();