In a mixing bowl, whip the heavy cream, powdered sugar, and vanilla extract until soft peaks form.
In another bowl, combine the sweetened condensed milk with half of the sliced bananas.
In serving glasses or bowls, layer the ingredients starting with a layer of crushed graham crackers.
Add a layer of the banana mixture.
Add a layer of whipped cream.
Sprinkle chocolate shavings on top.
Repeat the layers until the glasses are filled, finishing with a layer of whipped cream and a few banana slices on top.
Chill the trifles in the refrigerator for at least 1 hour before serving.