Melt butter in a large saucepan over medium-low heat.
Add in marshmallows and stir until melted, while tinting with green food coloring to reach desired shade.
Remove from heat add in Rice Krispies cereal and fold mixture until evenly coated. Let cool about 5 minutes.
Spray hands with non-stick cooking spray and shape about 1/3 cup to 1/2 cup of the mixture into into cones, while pressing firmly so they'll hold together.
Decorate with sprinkles, using the icing to get them to stick. Then put icing on the Reeses and place one under each tree.
Note if you want the icing to harden let them rest overnight, or you can just eat them right away.
Recipe source: adapted from Family Circle