Preheat the oven to 350°F.
Prepare two 9-inch round cake pans by greasing them well or lining the bottoms with parchment paper.
In a large mixing bowl, combine the yellow cake mix, eggs, instant vanilla pudding mix, drained mandarin oranges, orange extract, and oil.
Mix until the batter is smooth and fully combined.
Divide the batter evenly between the prepared cake pans.
Bake for 20 to 25 minutes, or until the cakes are fully baked and a toothpick inserted into the center comes out clean.
Remove the cake pans from the oven and allow the cake layers to cool in the pans for several minutes.
Transfer the cake layers to a wire rack and allow them to cool completely before assembling.
In a separate mixing bowl, combine the drained crushed pineapple with the instant vanilla pudding mix.
Stir until the mixture is evenly combined and begins to thicken.
Gently fold in the thawed Cool Whip until the topping is smooth and fully incorporated.
Place one cooled cake layer on a serving plate or cake stand.
Spread an even layer of the pineapple topping over the first cake layer.
Place the second cooled cake layer on top.
Spread the remaining pineapple topping over the top and sides of the cake.
Garnish with mandarin orange segments and pineapple pieces, if desired.
Refrigerate the cake until ready to serve.
Serve chilled.