MIX graham crumbs, butter and sugar; press onto bottom and up side of 9-inch pie plate. Set aside.
MIX marshmallows and milk in large microwavable bowl. Microwave on HIGH for 2 to 2-1/2 minutes or until marshmallows are completely melted, stirring after 1 minute. Refrigerate 40 minutes or until mixture is completely cooled.
GENTLY stir whipped topping and 3/4 of the chocolate into marshmallow mixture. Spoon into crust; top with remaining chopped chocolate.
REFRIGERATE 3 hours or until firm.