I've beat Zeromus with all the characters, and I've done everyone's trial except the twins (Palom and Porom) and Cid. The last trial I completed was Edward's trial. Now I've come across a room with a door on the left side and the right side leads to a ledge that you can't go down. If you examine the door it gives you a message saying that it's engraved with a symbol of a lifeless tree, but it doesn't prompt you to use any items on it. How the do I get past the door?