MongoClient.connect('mongodb://localhost', (err, client) => {
  assert.ok(client);
  const coll = client.db('test').collection('foo');
  const ordered = new Map([
    [ 'a', 1 ],
    [ 'z', 2 ],
    [ 42, 3 ]
  ]);

  coll.insert(ordered, (err, res) => {});
});