Bake cake according to package directions for a 9x13 cake. Let cake cool completely. Use a sharp knife to cut a tree shape out of the cake. Remove the sections that you aren't using and set aside.

Remove the tree by cutting into 3 large sections and use a spatula to move onto a large board or serving plate. Use the scrap pieces of cake to create a trunk and place at the bottom of the tree.

Frost the trunk with chocolate frosting.

Add green color gels to the white frosting and mix well. Spread onto the cake. Use the knife to create bough like shapes onto the frosting.

Decorate the cake with white pearl candies to create garland. Use black color gels and candy coated sunflower seeds to create a string of lights. Add additional candies to create ornaments.

Store leftover cake loosely covered at room temperature.