They do it every year, but they always forget how it goes together.
Slide the parts to move them so that they fit in the frame to make three perfect trees.
Parts are not allowd to overlap.
Start with the parts that have the red baubles attached to them.
It's easiest if you look at the parts that go on the right and left sides first.
Place the biggest part that has a bauble at the bottom-right of the tree decoration.
Place the large triangular part at the top-left of the tree decoration.
There are six parts remaining.
Place the two that are the same shape at the top.
It should be obvious where to put the parts with the baubles.
Not long now until the decoration is done!
Answer for 'O Christmas Tree!'
The answer is as follows.