All done using the English Paper Co Christmas pack (I bought a load in the sale - so this Christmas is purple purple purple chortle).
Largest box dimension is 7cm square (so you have 5 squares all 7cm square cut out of a single piece of card like a maltese cross and scored), middle layer is 6cm square and inner layer is 5cm square - the tree has a hmm is it a radius? not a circumference? anyway the measurement across the middle from one side of the circle to the other which probably has a name but I don't know what it is - is 5cm also which geometry makes about 4.5cm high (don't ask me, I guessed and fiddled until it worked with scrap paper!)
I don't have a pattern for it, Jayne at Puffin Crafts had made a big one with the tree made out of folded over ribbons and a larger gap between layers and she had toppers in each layer. I looked at it for a while then went home and made this little version with folded over paper for the tree.
PS Sigh I've just looked at everyone else's and it's supposed to be something else that's useful. Ooops! Oh well too late now, and anyway it was months ago, I doubt anyone will be checking!