1. Line a cookie sheet with waxed paper.
2. Pour the cereal into a 4-quart bowl. Set the bowl aside.
3. Place the butter and marshmallows in a 3-quart saucepan. Heat over low heat, stirring constantly, until the mixture is smooth. Remove from heat.
4. Stir in food color until the mixture is evenly colored. Pour the marshmallow mixture over the cereal and stir until evenly coated.
5. Lightly spray your hands with cooking spray. For each tree, shape about 1/4 cup of the cereal mixture into a Christmas tree shape on the cookie sheet.
6. Press the candies into the trees to decorate. Refrigerate until firm, about 1 hour. Store the trees in a loosely covered container.