So i'm trying to make a nice index but the numbers don't add up.

At this moment it's like this:

1. Chapter one .... 1
1.1 Sub ........... 2
2. Chapter two .... 3
1.2 Sub ........... 4

But it should be like this:

1. Chapter one .... 1
1.1 Sub ........... 2
2. Chapter two .... 3
2.1 Sub ........... 4

I hope I made myself clear with this.. This is my first time posting here.