How do I exit a node group? I selected a bunch of nodes that I wasn't using and that weren't connected and thought that I would see if I could group them. 

Well, Blender let me group them alright, but now there is a green background over the rest of my nodes and I cannot select any of them anymore. I deleted the nodes in the group because I couldn't figure out how to "ungroup" them and undo would not undo the grouping operation.

Does anyone have any idea how I can get things back to normal or do I need to start all over again?
You can press &#8633; Tab to switch in and out of a node group, or you can press the arrow button in the header to go to the parent node tree:



To ungroup nodes:


Go to the parent node tree
Select the group node
Press &#9095; AltG