In a bowl, combine crushed Oreo cookies and melted butter.
Press the mixture into the bottom of a 9x13 inch dish to form the crust.
In another bowl, beat the cream cheese and powdered sugar until smooth.
Fold in half of the whipped topping into the cream cheese mixture.
Spread the cream cheese layer over the crust evenly.
In a separate bowl, whisk together the chocolate pudding mix and milk until thickened.
Spread the chocolate pudding over the cream cheese layer.
Add the remaining whipped topping on top of the pudding layer.
Garnish with chocolate shavings or cocoa powder.
Cover and refrigerate for at least 4 hours before serving.