auto increment parent_no

Question

Hello sir, I am developing a project on multi level marketing in asp.net with c#.

I am in a problem to generate parent_no in database from asp.net. I have attached an image. 

 

My requirement is The first one who will register will be the parent and then who will register will be its child and like generation wise. Every parent will have only 2 Children. and so on the tree will increase. All this registration will be on asp.net web page. So I am facing problem to generate parent_no in asp page and for each two entries the parent_no will same then increment by 1 then same for two entries and then increment by 1 as the parent_no (image attached).

 

Thanking you

Sidhartha Patnaik