In a large mixing bowl, whisk together pudding mix and cold milk until smooth and thickened.
Stir in the sweetened condensed milk and vanilla extract until combined.
Fold in half of the whipped topping gently to keep the mixture light and fluffy.
In a trifle dish or large glass bowl, layer vanilla wafers along the bottom.
Add a layer of banana slices over the wafers, then spoon some pudding mixture on top.
Repeat the layers until all ingredients are used, finishing with pudding mixture on top.
Spread the remaining whipped topping over the pudding and smooth it out.
Chill for at least 3 hours before serving to let the flavors mingle.