I made these cupcakes for a friend over the weekend. They are plain chocolate cupcakes with vanilla wiss buttercream frosting. You could use another frosting, of course, but make sure it is not too soft or your trees will slouch and look all lumpy.
First I made the snow by piping a ring of white frosting around the edges of the cupcake and dipping it in white nonpareil sprinkles. You could use coconut instead. Don't worry if it's lumpy. It just adds to the "snowbank" effect.
Next, using a star tip, pipe the tree by piling the green frosting in a tight circle. Decorate your tree using whatever strikes your fancy. I used more nonpareils, some snowflake sprinkles, some beautiful edible gold star sprinkles and a blue ball on top.