Grease or spray a 9x13-inch pan and set aside.

In a large pan, melt butter and marshmallows over medium-low heat, stirring constantly. Once it almost smooth and melted, add green food coloring little by little until you achieve your desired tree color. Once completely smooth and perfectly green, remove from heat and stir in Rice Krispies. Continue to stir until all the cereal is coated.

Press evenly into prepared pan (I always spray my hand with nonstick cooking spray to do this, but you can also use a piece of wax paper). Immediately sprinkle with sprinkles. Let cool for at least 30 minutes.

Cut one cut down the middle of the pan (the long way). Then, cut each of those rows into triangles (you should have 4 scraps leftover, one at each side of each row).