When Homer is throwing a Frisbee up at Bart in the tree, wooden steps/ladder is seen on the tree, but this is not there when he shakes the tree and when Lisa climbs it.
After leaving the locker-room, Lisa, Tina, and Carrie exit the "Lugash's Gym" through a back exit door with an drawn on the outside. An exit bar is used to enable occupants to leave a building quickly (in emergencies) and without a key. One would never be installed on the outside.