The trees in Sylvan are scripted. When you click on one of them, the hero's level instantly increases without any further prompts. If one hero levels up at this tree, another hero won't be able to level up there anymore.
Maybe I did level up, but I'm not sure; I'm just confused by the message.
The hero doesn't care anyway; he's already level 35.
I always use Sigrid to click on the level-up spots; what's the point of the others doing it?