Firebase : How to add a node without auto generated key

The trick is to use set instead of push, example is below

 String normalizedUserName = getNormalizedUserNameForDBPath(email);
        String enterpriseRoot = normalizedUserName;
        DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference();
        String pathName = APP_NAME + "/" + enterpriseRoot + "/users";
        final DatabaseReference messagesRef = databaseReference.child(pathName).child(normalizedUserName);
        messagesRef.setValue(userdetails); 

=> Dont use push