Prepare the jello with the boiling water. Add the marshmallows, and let cool. Add the milk and stir. Fold in the fruit cocktail. At this point, you can choose to add the bananas here or slice on top after completely set. Pour into a jello mold or a 9 cake pan. When completely set, add the bananas (if you haven't already) and top with cool whip or whip cream.