Star

Step one for putting the Star on the top of the tree: step onto the chair while looking at Mum in order for her to get a good picture.
Step Two: reach forth your arm to the destination of the Star. And then pause so Mum can get a picture. Only after Mum has taken a good picture can you proceed.

Step three: once the Star is in place, look at Mum again so she can get a picture of both you and the star, which is now on the top of the tree.