Typography, paragraph styles numbering question

Hi there,

I'm working on a document that has numbering as follows:
(obviously going up numerically for each section)

6.     Heading goes here
6.1   Lorem ipsom
6.2   Lorem ipsom
6.3   Lorem ipsom

I can set a paragraph style to make sure all the section numbers/chapters follow on, so 1, 2, 3, 4 etc.
When I'm trying to set another paragraph style to say that I want the nested sections to be 6.1, 6.2, 6.3 etc, I am only able to choose A, B, C etc or roman numerals etc. How do I set my paragraph style to include the chapter number and be 6.1, 6.2, 6.3 etc?

Thank you!