Decorate cake. Prepare five decorating bags separately with red-orange, orange-red, dark yellow, orange and golden yellow icing. Cut 1 in. hole in tip of each bag.
Starting with red-orange icing, pipe two even rows of icing around bottom of cake. Continue piping rows, working towards lightest shade (orange-red, orange, golden yellow, yellow). Ice top of cake with yellow icing.
Using icing smoother, smooth out icing, letting colors lightly blend together.
Prepare decorating bag with tip 4 and reserved black icing. Pipe trees around cake.
Helpful Hint: If needed, draw trees on your cake with a toothpick first before piping.