To a large mixing bowl, measure out the rice cereal. Set aside. Spray a 9 x 13" pan with non-stick baking spray. Set aside.

In a separate microwave safe bowl, add the marshmallows and butter. Microwave 1 minute, stir to incorporate the butter. Microwave again for 30-45 seconds until the marshmallows are nearly melted. Stir well until smooth and the marshmallows and butter are melted together.

Add about 60 drops of green food coloring to tint the marshmallow mixture bright green. Stir well so that the marshmallow mixture is completely green. Pour into the cereal.

Working quickly, stir the marshmallow mixture and cereal together so that the cereal is completely coated. Pour the cereal into the prepared 9 x 13" pan. Spray your hands with non-stick spray and press the cereal evenly and firmly into the pan. Sprinkle the cereal treats with the Christmas sprinkles. Let the treats cool for 15-30 minutes to room temperature.

Invert the treats onto a large cutting board, or baking sheet, flipping the treats over with another baking pan, so that the sprinkle side is facing up. Cut the treats into 3 long strips, each 3" wide and 13" long. Cut each long strip into triangles.

Separate each triangle and decorate. Use the gel icing to act as a glue to stick the stars at the top of each tree. Also use the icing to stick the halved peanut butter cups onto the bottom of each tree to represent the tree trunks. Use the gel icing as the Christmas light strings, and place the mini M&M's as the Christmas lights.

Let the treats set out for 1-2 hours to let the icing dry. Serve and enjoy right away.