Known bug. It will go away if you level up. Happened to me.
Leveling didnt help it. Did you mean skillup? Cant do that since Im at 100. It might be a display bug though. The number under the tree says its 25 but when I click the tree it shows 100, plus it did let me perk the top perk just now. Also, Aela wont train me so that makes me think my skill is 100. But I still could have 100 skill but lowered value due to sickness and it would be the same. Console doesnt seem to have any feature that would help. Dispelallspells didnt fix it. Console cant raise my skill since its already 100. I guess Ill try running around and see if I can kill stuff. Otherwise, I dont know how to tell if its real or just a display error.