In a mixing bowl, whisk together the pudding mix and cold milk until thickened, about 2 minutes. Gently fold in 1 cup of the whipped topping until smooth.

In a large glass trifle dish or individual serving cups, layer a third of the Christmas Tree Cake pieces, followed by a layer of the pudding mixture and a sprinkle of berries. Repeat the layers until all ingredients are used, ending with a pudding layer.

Top with the remaining whipped topping.

Serve immediately or chill for up to 2 hours before serving for the best texture. Just before serving, draw wavy lines over the top with red icing. Sprinkle with green sprinkles if desired.