Microwave caramels and milk in microwaveable bowl on HIGH 2 min.; stir. Microwave 2 min. or until caramels are completely melted and sauce is well blended, stirring after each minute. Add dry pudding mix; whisk 2 min. Cool 15 min. Gently stir in 1-1/2 cups COOL WHIP. Refrigerate 20 min. or until chilled.
Slice bananas. Cut cake into 3 horizontal layers; stack on plate, filling layers with caramel sauce and bananas.