Make the frosting: In the bowl of a stand mixer, beat the powdered sugar and butter, starting on low speed and working your way up to high, until incorporated, about 1 minute. Add the milk and beat on high until smooth and fluffy, 30 seconds to 1 minute more.
Set aside ¼ cup of frosting aside. Divide the remaining frosting among four bowls; leave one bowl white. In a second bowl, add 10 to 12 drops green food coloring and mix well with a spatula until no streaks remain. In the third bowl, add 5 to 6 drops green food coloring and mix well. In the fourth bowl, add three to 4 drops green food coloring and mix well. Adjust colors as needed. To the reserved ¼ cup frosting, add 3 to 4 drops golden-yellow food coloring; mix well.
On a large cutting board, tray, or flat serving platter, arrange the cupcakes in the shape of a Christmas tree, starting with one row of 5 cupcakes and decreasing the number of cupcakes as you move upward. Above the top, place one cupcake to make the star. At the bottom, place two cupcakes in the center to make a base.
Frost the base cupcakes with the white frosting. Frost the bottom row with the darkest green frosting. Frost the middle two rows with the medium-green frosting. And frost the top three cupcakes at the peak of the tree with the lightest green frosting. Frost the star cupcake with the yellow frosting.
Dust the yellow cupcake with the white sparkling sugar. Dust some of the perimeter of the other cupcakes with the green sparkling sugar. *Get the recipe for vanilla cupcakeshere.