Bake the sugar cookies according to the package directions. Remove from the oven and allow them to cool completely. If the cookies are even slightly warm, the frosting will melt and won’t hold its shape.

In a medium bowl, mix together the vanilla buttercream frosting and confectioners’ sugar until smooth. The powdered sugar thickens the frosting so it can be piped tall like a tree. Add green food coloring a little at a time until you reach your desired shade.

Transfer the frosting to a piping bag with the tip cut off, or use a zip-top bag with one corner snipped.

Pipe a circle of frosting about ½ inch from the edge of each cookie. Continue piping smaller circles on top of each other, working inward and upward until you form a peak.

Place a yellow mini M&M at the top like a star, then decorate the frosting with red and green mini M&Ms for ornaments.

Let the cookies set for 10–15 minutes before serving.