<?php
require 'vendor/autoload.php';
$con = new \MongoDB\Client('mongodb://localhost:27017');

$res = $con->db->collection->insertOne(
    [ '_id' => 1, 'x' => 1 ],
    [ 'writeConcern' => $wc ],
);

$wc = new MongoDB\Driver\WriteConcern( MongoDB\Driver\WriteConcern::MAJORITY );

$wc = new MongoDB\Driver\WriteConcern( MongoDB\Driver\WriteConcern::MAJORITY, 10000 );