Is that multi master replication is not recommended to do ?
No, it is not recommended, as it has a very, very narrow use case, and comes with a lot of drawbacks. Sure, you COULD configure your car to also be able to ride across the river like a boat, but it's far easier to use a bridge, or a barge. And now your car is harder to care for, and has a lot more ways in which it could break.
If we can do, can I get any resource for implementing that on PostgreSQL which is open-source?
You still have not told us your use case. That can help us to guide you to the right solution. But for totally open source solutions there are not many out there. Here are some:
