1Heat oven to 375°F. In medium bowl, stir cookie mix, butter and egg until soft dough forms. Shape 3 (1/4-cup) balls from dough. Shape 3 more balls, using 3 level tablespoons dough for each. Place all 6 balls on ungreased cookie sheet. Bake 9 to 11 minutes or until edges are light brown.
2Meanwhile, shape 3 balls using 2 tablespoons dough for each ball. Shape 3 balls, 1 1/2 inches in diameter. Place all 6 balls on ungreased cookie sheet. Bake 7 to 9 minutes or until edges are light brown.
3Continue with remaining dough to make 3 balls of each of the following diameters: 1 1/4 inches, 1 inch, 3/4 inch and 1/2 inch. Place on ungreased cookie sheet. Bake 5 to 7 minutes or until edges are light brown. Cool completely, about 30 minutes.
4Heat frosting in microwavable bowl uncovered on High 30 seconds, stirring every 10 seconds, until frosting can be stirred smooth and fluid. Each tree will be a stack of 8 different size cookies. To assemble 3 trees, stack cookies on serving platter, starting with largest size cookie on bottom, and stacking each smaller size cookie on top, spreading frosting between each layer. Drizzle remaining frosting over trees, and garnish with sprinkles. Sprinkle powdered sugar on platter to look like snow.