This settles it!
The Treant isn't supposed to catch on fire.
Once you accept the bird and cage quest, DON'T do it just yet.
Fool around and get the message to meet Kayanna beyond the trees. Obviously you do need the pine cone to get past the Treant. Once you get the necklace from her, go ahead and do the royal seal pieces and get thrown in jail. Before doing the moonshiner quest for Raymond, instead go get the bird cage for the thief master and give it to him. Now you can walk past the Treant without igniting it. You can go in the fortress but you just get thrown back out. Seems as if the bird cage quest causes the Treant to burn if you go there before meeting Kayanna. This appears to be a major bug to fix while playing as a Rogue.
So just continue with the Moonshiner quest!