Whip the whipping cream to soft peaks, adding the sweetened condensed milk in a steady stream, continuing to whip until the cream reaches hard peaks.
Layer 13-16 chocolate chip cookies in the bottom of a 9-inch by 13-inch rectangular baking dish, topping them with one-third of the whipped cream mixture.
Sprinkle one-third of the M&Ms over the whipped cream mixture, and top with the Oreo cookies.
Add another layer of the whipped cream mixture, more M&Ms, and another layer of chocolate chip cookies.
Add the final layer of the whipping cream mixture, topping it with some crushed Oreos and the remaining M&Ms.
Chill the cake in the fridge overnight (for 12-18 hours) until ready to serve.