ID:2685604
 
(See the best response by Kozuma3.)

Problem description:

I don't know what happened, it worked fine and then suddenly the icons weren't showing up in the tree while editing the map. I cannot figure out how to reverse it.

Everything else works fine, the icons on the side of the tree just aren't showing up.

Best response
Do you have "Show Icons" at the bottom of it enabled?
Wow I feel stupid, I didn't even see that box there and I have no idea how I disabled it. Thanks!