Preheat the oven to the baking temperature indicated on the box of brownie mix.

Prepare a 9x13-inch baking pan by lining it with parchment paper, leaving overhang along the sides to make it easier to lift the brownies out of the pan after baking.

Spread the brownie batter evenly into the prepared baking pan, then bake according to the package directions. Remove from the oven and cool the brownies to room temperature in the pan.

Pour the heavy cream into a medium microwave-safe bowl and heat in the microwave on high for 60-90 seconds until hot. Add the white chocolate chips and stir until completely melted, then mix in green food coloring until your desired color is reached.

Pour the frosting over the brownies and spread out evenly. Sprinkle the candy-coated mini chocolate chips all over top of the frosting.

Place the pan of frosted brownies in the refrigerator to chill until the frosting is completely set; about 1 hour.

Once set, lift the brownies out of the pan. Use a sharp knife to cut the sheet of brownies longways across into three strips. Cut each strip into triangles to resemble Christmas trees.