Christmas Tree Cake
Ingredients:Baking spray with flour2 (15 1/4-oz.) pkg. devil's food cake mix (such as Duncan Hines)4 cups (2 lb.) unsalted butter, at room temperature1 (2-lb.) pkg. powdered sugar1 teaspoon vanilla extract½ teaspoon kosher salt1 (0.67-oz.) tube green food coloring gel½ teaspoon blue food coloring gel, or more to preference¼ teaspoon yellow food coloring gel, or more