**Prepare the Pudding:** In a large mixing bowl, whisk together the sweetened condensed milk and ice-cold water until combined. Add the instant pudding mix and beat with an electric mixer on medium speed for 2 minutes. Cover and refrigerate for at least 4 hours or overnight.

**Whip the Cream:** In another mixing bowl, whip the heavy cream on medium-high speed until stiff peaks form.

**Fold the Cream:** Gently fold the whipped cream into the chilled pudding mixture until fully incorporated and smooth.

**Assemble the Layers:** In a 9x13-inch dish or trifle bowl, spread a layer of pudding mixture on the bottom. Top with a layer of Nilla wafers, followed by a layer of sliced bananas. Repeat the layers until all ingredients are used, finishing with a layer of pudding on top.

**Chill:** Cover the dish tightly and refrigerate for at least 4 hours or up to overnight to allow the flavors to meld and the wafers to soften.

**Serve:** Garnish with additional Nilla wafers or banana slices just before serving.