MyBB Community Forums

I converted my forum from PHPB3 to MyBB and I have some trouble to configure some permission.

On my board I have 2 groups A & B. A can see all child forum and B can only see a subset.

Exemple

Member of group A can see that :
Public Forum
+ Public SubForum 1
+ Public SubForum 2
Private Forum
+ Child Forum for A & B
+ Child Forum for A

Member of group B should see that :
Public Forum
+ Public child Forum 1
+ Public child Forum 2
Private Forum
+ Child Forum for A & B

Right now all I managed is to hide all the Private forum to B, or to show them all the child forum.
How can I show them the child forum they are allowed to go in, but hide the other ?

No one ?

You can change the permissions in ACP - Forum and posts- Then edit the particular forum with permissions.