Getting members (users) of groups of an OU

Question

Hi there,
i am trying to retrieve the members of groups of each OU under one OU.
First of all here is a small and partial overview of the given DS:
D2    //"root" OU
|->20 // sub OU
     |->20_general_w // group
     |->20_general_r // group
     ...
     |->Maxine Sample // user
|->21
     |->21_general_w
     |->21_general_r
     ...
     |->Jim Kirk
So far i am able to get all sub OUs, Groups and Users from D2, but i have no idea how to sort the data in a structured way, showing foreach OU their groups with their members. Unfortunately i am not that fit with ldap and queriing/filtering, so that i have no clue in wich way ou<->groups<->users are interacting...
Does anyone have an idea how the loops and intersections have to be set up to retrieve an appropriate result?
Best
Snakey