Whisk together the cold milk and instant chocolate pudding mix until well incorporated and the mixture begins to thicken. Cover and refrigerate until ready to use.
Using a stand mixer or electric hand mixer, beat together the whipping cream, peanut butter and confectioners' sugar until stiff peaks form. Gently fold in the chopped peanut butter cup candies, reserving 1/4 cup for the top.
To assemble the trifle, loosely break up the brownie bites. If the trifle dish is even at the bottom, place a layer of broken brownies over the bottom of the dish. (If the trifle dish has a dip in the center, spread 1/2 cup chocolate pudding into the dip to even it out before starting with an even layer of brownies.) Top the brownies with 1 cup of pudding, spreading it to an even layer with an offset spatula. Follow by spreading 1 1/2 cups of the peanut butter whipped cream atop the pudding layer. Repeat twice with the remaining brownie bites, pudding and whipped cream, creating 9 layers total and ending with a whipped cream layer. Sprinkle with the remaining chopped peanut butter cups.
Cover loosely with plastic wrap and refrigerate for at least 4 hours and up to overnight before serving.