I am working on a project which user registration multiples like this.
1st Month -> 1 user
2nd Month -> 4 users comes under the above user
3rd Month -> 16 users (i.e, 4 users comes under each 4 users above )
4th Month -> 64 users (i.e, 4 users comes under each 16 users above )

eg: 1
    2 | 2
    8 | 8
   32| 32

ve devam ediyor ...

Please give me an advice, how to store this in database. Thanks in advance.