Frozen Root Beer Float Pie

tub (8 ounces) frozen reduced-fat whipped topping (such as Cool Whip), thawed

cold diet or regular root beer (I used regular)

fat-free or regular milk

Root Beer Extract to taste. (strength can vary greatly by brand)

package (4 serving size) instant vanilla pudding mix

graham cracker crust (store bought or homemade)

Maraschino cherries