How do I put my Body group into my Armature group? This is what my groups currently look like



This is what I'd like them to look like



I've tried simply clicking and dragging the Body onto the Armature text in hopes that the Body would go into that folder with no luck. 

If anyone could help me find the answer I'm looking for I would appreciate it.

regards,
Make sure to click and drag the ICON next to the group name. Not the TEXT.

Click and drag the ICON of the group onto the other group.