**Prepare the pudding**
In a mixing bowl, whisk together the pudding mix and cold milk until smooth and thickened, about 2 minutes. Set aside.
**Layer the trifle**
Begin layering the trifle in a large trifle dish or glass bowl. Start with a layer of cubed cake or brownies at the bottom.
**Add pudding and Oreos**
Spread a layer of pudding over the cake, followed by a layer of crushed Oreos.
**Add whipped topping**
Spread a layer of whipped topping over the crushed Oreos. Repeat the layers until all ingredients are used, finishing with a layer of whipped topping.
**Garnish**
Sprinkle the top with crushed Oreos and drizzle with chocolate syrup, if desired. Garnish with whole Oreo cookies for a decorative touch.
**Chill and serve**
Cover the trifle and refrigerate for at least 2 hours, or overnight, to allow the flavors to meld. Serve cold and enjoy!