I need to use Microsoft Active Directory in order to cluster a set of
users hierachically.
The problem is that i need some users to exist into different clusters
of different height at the same time.
At first i tryied to use Security Groups, but i cannot find a way to
organize hierachically security groups(i can not make a security group
member of a non built-in custome security group).
As a can find the only way to use Active Directory for this is to use
Organization Units, but i cannot add the same user to different
Organization Unit at the same time.
A walkaround to this is to create at each organization unit a security
group where i will store my users, but this is not so flexible.
Is there another approach?

Create user group and add all bembers to this group. Then U can view
all members in this group.