Prepare and bake the cupcakes according to the directions on the box. Allow them to cool before decorating.
In a medium mixing bowl, add the room temperature melted butter. Mix on medium speed with a hand mixer for 1 minute.
Add half of the sugar to the bowl and mix until combined. Then add the remaining sugar and mix again.
Add the vanilla extract, 3 drops of green food dye, and 1 tablespoon of milk. Mix until the color is incorporated and the mixture is smooth. If needed, add another tablespoon of milk until the desired consistency is reached.
Fill a piping bag fitted with a piping tip with the frosting and pipe it onto the cupcakes.
Place mini M&M's all over the frosting to create the lights. Use red and green for a themed tree or all of the colors for a multicolored tree. Place an edible star at the top of the tree.
Notes
Feel free to use a tub of cream cheese frosting and green food coloring instead of making your own.
And if you can't find star sprinkles, get creative with a yellow M&M or gumdrop for the star!
Food dye darkens over a couple of hours, so don’t add too much when blending it in with the frosting.