How can i bulk create in django rest serializer

Yes you do need to override create and update methods of your UserSerializer.

I've spent a lot of time trying to make nested writable serializers work with DRF 2.x and the more I fixed issues the more issues were risen with corner use cases.

Therefore Tom decided that it should be left up to the developer to handle the creation and updates.

The documentation provides an example for a 1 nesting level creation but it's the same for update and/or with more nesting level