The bulk write documentation at https://docs.mongodb.com/ruby-driver/master/tutorials/ruby-driver-bulk-operations/#insert-many gives an example of using insert_many with bulk writes. I tried it and it did not work. It seems insert_many is not actually a thing and instead a bunch of insert_ones should be used.
If so, the documentation should be updated to indicate that only insert_one is a defined operation.
As part of this ticket the integration tests in the driver should be audited to verify that everything the documentation claims to be supported via bulk writes is tested in the test suite.