In a large mixing bowl, whisk together the instant pudding mix and cold milk until smooth and thickened.
Add the sweetened condensed milk and mix until well combined.
Fold in the whipped topping gently until fully incorporated.
In a 9x13-inch dish, layer vanilla wafers on the bottom.
Add a layer of banana slices over the wafers.
Spread half of the pudding mixture over the bananas.
Repeat layers with the remaining wafers, bananas, and pudding.
Cover and refrigerate for at least 4 hours or overnight before serving.