How to Map a List of Java Entity to Multiple MongoDB Collections in Spring Data?

Currently, we're looking for a solution to save the List of User entity into multiple MongoDB collections at the same time (i.e. db_users and on db_users_legacy). Both collections are in the same database.

I have followed this link. In this link they are saving single User entity into two different collections. But , I want to insert list of User entity into two different collections. I tried to insert using for loop. But it is taking time to iterate entire list and save object one by one.

 @Override
    public void saveUser(List<User> userList) {
     for(User user: userList) {
        mongoTemplate.save(user, "db_users");
        mongoTemplate.save(user, "db_users_legacy");
       }
    }

Is there any way to insert List of User entity into two different collections at one shot without using any for loop ?