class First extends BaseEntity {}
class Second extends BaseEntity {}

class BaseEntity {
   Long id;
}

    @Repository
    interface FirstRepository  extends MongoRepository<First, Long> {}

    @Repository
    interface SecondRepository  extends MongoRepository<Second, Long> {}

    public void testRepositories(){
        List<? extends MongoRepository<? extends BaseEntity, Long>> repositories = Arrays.asList(
                firstRepository,
                secondRepository,
                thirdRepository
        );

        for (MongoRepository<?, Long> repository : repositories) {
            repository.save(new BaseEntity(1L));
        }
    
    }