Root Beer Float Pie

Root Beer Float Pie
Ingredients

1 tub (8 ounces) frozen reduced-fat whipped topping (such as Cool Whip), thawed
3/4 cup cold diet or regular root beer (I used ...regular)
1/2 cup fat-free or regular milk
Root Beer Extract to taste. (strength can vary greatly by brand)
1 package (4 serving size) instant vanilla pudding mix
1 graham cracker crust (store bought or homemade)
8 Maraschino cherries