Gryffindor? Rush over to the tree, climb up to attempt to rescue the kitten.
Hufflepuff? Using teamwork, grab an end of the limb and have many people hang on to bend it low enough so that someone can be lifted up high enough to reach the kitten (and the stuck Gryffindor).
Ravenclaw? Pick some wild catnip and find a ladder and attempt to entice the kitten down. (The Gryffindor is also out of reach of the ladder by now.)
Slytherin? Borrow someone's cellphone and call the fire department to come and effect the rescue. Take all the credit for being the level-headed one while the rest of the people were rushing about in general distraction.