Line a baking tray with parchment paper. Spray or butter the paper.
Melt the butter in a large stock pot. Once melted, add the marshmallows and stir constantly until mostly melted.
Add the food coloring and stir until incorporated. Add more until you reach a dark green color.
When all the marshmallows are dissolved, take the pot off the heat and add the Rice Krispies.
Fold the cereal in with a spatula until evenly coated and mixed.
Pour the mixture onto the baking tray. Put some butter on your hands and pat down the Rice Krispies until uniform and even. Allow to cool for an hour.
Use a knife or cookie cutter to cut out the trees. Decorate as you like.
Notes
Use a fresh bag of marshmallows for this recipe. We all have half used bags in the pantry but they will not melt as well. Grab a new bag at the grocery store.
Try adding a teaspoon of vanilla extract to the melted marshmallows. It adds more flavor.
You can coat your fingers or spoon in butter to keep the rice krispies mixture from sticking to your hands while you are pressing it into the baking tray. You can also wet your finger with water and press the mixture into the baking sheet both options should keep your hands clean.
Add a cup of mini marshmallows to your mixing bowl as you are stirring the cereal into the melted marshmallows. The mini marshmallows will melt and add extra little texture and chewiness.