INSERT RESULT {
  result: { ok: 1, n: 2 },
  ops: [ { _id: 1 }, { _id: 2 } ],
  insertedCount: 2,
  insertedIds: [ 1, 2 ]
}

INSERT RESULT BulkWriteResult {
  ok: [Getter],
  nInserted: [Getter],
  nUpserted: [Getter],
  nMatched: [Getter],
  nModified: [Getter],
  nRemoved: [Getter],
  getInsertedIds: [Function],
  getUpsertedIds: [Function],
  getUpsertedIdAt: [Function],
  getRawResponse: [Function],
  hasWriteErrors: [Function],
  getWriteErrorCount: [Function],
  getWriteErrorAt: [Function],
  getWriteErrors: [Function],
  getLastOp: [Function],
  getWriteConcernError: [Function],
  toJSON: [Function],
  toString: [Function],
  isOk: [Function]
}

const { MongoClient } = require('mongodb');

MongoClient.connect('mongodb://localhost:27017/test', (err, db) => {
  if (err) {
    return console.log('MONGO CONNECTION ERR');
  }

  db.collection('users').insertMany([{_id: 1}, {_id: 2}], (err, result) => {
    if (err) {
      console.log('WRONG INSERT', err);
    }

    console.log('INSERT RESULT', result);
  });
});