Numbered headings like 2.1.1.1 etc

[seanspotatobusiness]

I'm trying to make it so my headings are like:

Chapter 2 Blah blah

2.1 Blah blah blah

dfdfsfsf dfhdfgf sdgsdgdgf

2.2 Blah blah

ggdggd dgdfggd sdgdgg

but when I tried to apply numbers to heading level 2, the numbers failed to restart at chapter 2 (as seen in the screenshot) and also don't include the previous heading number. I'd like it so that heading level 4 with be like: 2.1.1.1 etc. I would, however, like my chapter headings to stay starting "Chapter 2" rather than "2. Chapter 2" or whatever.

I can sort of apply the numbering I want by moving the cursor into a heading and selecting the appropriate "multilevel list" format but that changes the level 1 headings from "Chapter 2" to "2." and if I try to modify the format of heading level 1 then all the subsequent subheadings change from 2.whatever to 1.whatever.

Does anyone know what I mean and how to achieve it? Thanks!