In a small bowl, mix 2 cups crushed cookies and butter. Press onto bottom of a greased 9-in. springform pan. Refrigerate until ready to use., In a large microwave-safe bowl, microwave chocolate on high just until melted; stir until smooth. Cool to room temperature. , In another bowl, beat cream and confectioners' sugar until stiff peaks form; fold 4 cups into chocolate mixture. Spread over crust. Spread remaining whipped cream over top. Cover and refrigerate until set, about 3 hours. If desired, garnish with additional Oreos.