Preheat the oven to 200ºc/180ºfan and line a large baking tray with parchment paper
Grab your two sheets of puff pastry and cut off the corners to make long triangles
(off cuts can make something else, or be frozen for another time)
Lay one triangle onto the lined baking tray
Spread the nutella on top (may be easier to melt it first)
Add the second triangle of pastry on top
Cut branches on the tree by cutting through the sheets of pastry and nutella, in inch sized rows, from top to bottom (look at the pictures for reference).
Make sure to leave an inch column down the middle of the tree so it's still connected.
Carefully twist each branch a few times to create swirls in the pastry
Once swirled, brush the exposed pastry with the beaten egg
Bake in the oven for 20-25+ minutes, until golden. Once baked, dust with icing sugar.
Notes
You can do the same idea as a giant snowflake. Cut two large circles, and follow the same idea, but keep a circle in the middle uncut
This is best served fresh
As per the post, filling can be whatever spread you prefer, or a combination! Biscoff and nutella work wonders together.