Preheat your oven according to the cake mix's directions (normally, it is 350 degrees F). Coat both pans with your tablespoon of butter and sprinkle with flour, ensuring that you're coating each pan evenly and thoroughly.
In a medium-sized bowl, add all the necessary ingredients for your cake and mix! Once your batter is formed, pour into each pan. Bake according to the cake's directions.
Once the cake has baked, remove from pan and let it cool completely on a wire rack.
Place both cooled cakes on a clean working surface. Using your Christmas tree cookie cutter, cut out tree shapes and set aside.
Now's the time for some buttercream. To make it, use an electric mixer and beat your stick of butter, confectioners' sugar, milk on slow speed. Gradually increase it to high. Once the buttercream forms (it'll be smooth and form semi-stiff peaks), add green gel food coloring. Mix until completely tinted.
Attach your #32 frosting tip to a frosting bag. Scoop buttercream in the bag and frost each mini cake.
Add a dab of brown decorating frosting to the bottom of the tree to create its "trunk."