The cherry bomb tree is in the greenhouse (top of the tall tower
on Balding Avenue), all the way to the bottom right. You use it to
blast the cage holding the third spy. (see related question)
Enter the tube on the roof of the tall building (you will have to pass the guard and go to the other roof on your left, then back). After go in, go down and to the right and there is a plant called the Cherry Bomb Tree.