1Heat oven to 350°F (325°F for dark or nonstick pan). Line 9-inch square pan with foil so foil extends about 2 inches over sides of pan. Grease bottom only of foil with shortening or cooking spray.
2Make brownie mix as directed on box for 9-inch square pan. Cool completely, about 1 1/2 hours. Remove from pan by lifting foil; peel foil away. To cut brownie into triangles, cut into 3 rows. Cut each row into 5 triangles (See diagram below in Expert Tips). Save smaller pieces for snacking.
3Stir food color into frosting. Spoon frosting into small resealable food-storage plastic bag; partially seal bag. Cut off tiny bottom corner of bag. Squeeze bag to pipe frosting over brownies. Sprinkle with decors.
4Break off curved end of candy cane; insert straight piece into bottoms of triangles to make tree trunks.