For the pineapple cream filling: Combine instant pudding and heavy cream in the bowl of a stand mixer fitted with the whisk attachment. Mix on medium speed till thick and fluffy. Add in the crushed pineapple and mix till combined.
For the Cake: Stack all layers of cake with about 1/3 cup of pineapple cream filling spread between each layer, starting with one 5-inch round on the bottom, the three 6-inch rounds in the middle and ending with the last 5-inch round on the top. Cover cake in a thin layer of yellow buttercream and chill for 30 minutes.
Finish with a thick layer of yellow buttercream over the entire cake. Using the edge of a spoon or offset icing spatula, a chop stick, etc., create a criss cross diamond pattern over the entire cake.
For the Leaves: In the bowl of a stand mixer fitted with the whisk attachment, beat powdered sugar, meringue powder and warm water till stiff peaks form (about 5 to 7 minutes). If icing is too thick, add more warm water, 1 teaspoon at a time, till desired consistency is reached. Add green food coloring and mix till fully incorporated. Add royal icing to a piping bag fitted with a small round tip.
Place wax paper over leaf templates. Using the template as your guide, outline and fill in the leaves with the royal icing. Carefully move and position the wax paper with your piped leaves over a paper towel roll, with the tips of the leaves over the roll and the bottom of the leaves flat against the counter. Place a piece of the cake wire at the bottom of each leaf about an inch in. You can tape the paper towel roll and wax paper down if necessary. Let leaves dry for at least 4 hours. Gently peel the leaves from the wax paper when ready to use.
Place the prepared leaves onto the top of the cake, starting with the tallest ones in the center, and ending with the smallest on the outside.