Get All users from multiple AD Group Members

I need to get a list that shows all the users associated with a set of group members.

So if I have a security group for example>

TOP-Group 

And TOP-GROUP has 3 other member groups. 

1-GRoup, 2-Group, 3-Group

How can I get a list of all the users in TOP-Group, 1-GROUP, 2-GROUP and 3-GROUP and eliminate the duplicates?

I Assume this is possible in POWERSHELL. 

Thanks if anyone can help.