How do you change the core forum module to only show a certain depth? I am using the core forum module. If I have this forum structure:

- A1
 - A2
  - A3
- B1
 - B2
  - B3
- C1
 - C2
  -C3


I want it to show A1, B1 and C1. As well as A2 and B2. But not A3, B3 and C3. 

I checked the forum-list.html.twig file, but before I start hacking away, I was wondering if there isn't a more obvious hook of some sort I could use to do this?
If you want to change list of forums using hook try hook_preprocess_HOOK something like like 

function MYMODULE_preprocess_forum_list(&amp;$variables) { 
// dump here forums and search for the forum you want to remove and unset it . 
 dpm($variables['forums']); 
}