docs: function bulkWrite(coll, operations, options, callback) {
    // Add ignoreUndfined
    if (coll.s.options.ignoreUndefined) {
      options = Object.assign({}, options);
      options.ignoreUndefined = coll.s.options.ignoreUndefined;
    }
  
    // Create the bulk operation
    const bulk =
      options.ordered === true || options.ordered == null
        ? coll.initializeOrderedBulkOp(options)
        : coll.initializeUnorderedBulkOp(options);
  
    // Do we have a collation
    let collation = false;
  
    // for each op go through and add to the bulk
    try {
      for (let i = 0; i < operations.length; i++) {
        // Get the operation type
        const key = Object.keys(operations[i])[0];
        // Check if we have a collation
        if (operations[i][key].collation) {
          collation = true;
        }
  
        // Pass to the raw bulk
        bulk.raw(operations[i]);
      }
    } catch (err) {
      return callback(err, null);
    }
  
    // Final options for retryable writes and write concern
    let finalOptions = Object.assign({}, options);
    finalOptions = applyRetryableWrites(finalOptions, coll.s.db);
    finalOptions = applyWriteConcern(finalOptions, { db: coll.s.db, collection: coll }, options);
  
    const writeCon = finalOptions.writeConcern ? finalOptions.writeConcern : {};
    const capabilities = coll.s.topology.capabilities();
  
    // Did the user pass in a collation, check if our write server supports it
    if (collation && capabilities && !capabilities.commandsTakeCollation) {
      return callback(new MongoError('server/primary/mongos does not support collation'));
    }
  
    // Execute the bulk
    bulk.execute(writeCon, finalOptions, (err, r) => {
      // We have connection level error
      if (!r && err) {
        return callback(err, null);
      }
  
      r.insertedCount = r.nInserted;
      r.matchedCount = r.nMatched;
      r.modifiedCount = r.nModified || 0;
      r.deletedCount = r.nRemoved;
      r.upsertedCount = r.getUpsertedIds().length;
      r.upsertedIds = {};
      r.insertedIds = {};
  
      // Update the n
      r.n = r.insertedCount;
  
      // Inserted documents
      const inserted = r.getInsertedIds();
      // Map inserted ids
      for (let i = 0; i < inserted.length; i++) {
        r.insertedIds[inserted[i].index] = inserted[i]._id;
      }
  
      // Upserted documents
      const upserted = r.getUpsertedIds();
      // Map upserted ids
      for (let i = 0; i < upserted.length; i++) {
        r.upsertedIds[upserted[i].index] = upserted[i]._id;
      }
  
      // Return the results
      callback(null, r);
    });
  }