In a large mixing bowl, whisk together the pudding mix and cold milk until it thickens slightly.
Stir in the sweetened condensed milk until smooth.
Fold in the whipped topping until fully combined.
In a serving dish, layer vanilla wafers, banana slices, and pudding mixture. Repeat layers until all ingredients are used, ending with pudding on top.
Cover and refrigerate for at least 4 hours before serving to allow flavors to blend.