Bake the chocolate cake.
Prepare the cake batter according to the package directions, using the eggs, water, and oil specified.
Pour into a greased baking pan of the size recommended on the box. Bake at the listed temperature until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Let the cake cool briefly in the pan, then turn out onto a wire rack. Cool completely before assembling.
Prepare the pudding.
In a bowl, whisk the instant chocolate pudding mix with the cold milk for about 2 minutes, following the package directions.
Refrigerate for about 5 minutes, or until thickened.
Whip the cream.
In a separate bowl, beat the cold heavy cream, powdered sugar, and vanilla until stiff peaks form. Stop once the cream holds its shape.
Prepare the cake layers.
Cut the cooled cake into cubes or slice it horizontally into layers that fit your serving bowl. Cubes work especially well for filling gaps in a trifle dish.
Assemble the first layer.
Arrange half the cake in the bottom of a trifle bowl.
Top with half the chocolate pudding, half the fresh cherries, half the cherry pie filling, and half the whipped cream.
Repeat.
Repeat with the remaining cake, pudding, fresh cherries, pie filling, and whipped cream, finishing with whipped cream on top.
Decorate and chill.
Finish with shaved chocolate and additional cherries. Cover and refrigerate for at least 2 hours before serving.