Preheat the oven to 350°F. Lightly grease a 9×13-inch baking dish.

In a large bowl, beat together the cake mix, pumpkin purée, eggs, and water on low speed until well combined. Fold in pecans if using.

Pour into the prepared baking pan and bake for approximately 30 minutes, or until the top springs back when touched and a toothpick comes out completely clean. Let cool.

While the cake is baking, make the pudding according to package directions and whip the cream with sugar and vanilla until doubled in volume.

Cut the cooled cake into cubes. Place a layer of cake pieces in the bottom of a large trifle dish or bowl.

Spoon half of the cheesecake pudding over the cake, spreading it evenly. Add one-third of the whipped cream, smoothing it over the pudding.

Repeat, layering more cake, pudding, and whipped cream until the dish is filled. Finish with a final layer of whipped cream and garnish with pecans, if desired.

Refrigerate for at least 1 hour before serving.