Knead for around 8 minutes or so until the dough is elastic and smooth. Place back in the bowl, cover, and leave to rest in a warm place for about 30 minutes.
In the meantime, prepare the filling: Beat the butter, sugar and vanilla sugar together until nice and smooth. Set to one side.
Knock back the dough and divide into two roughly equal-sized bits. Roll out the first into a rectangle shape on a sheet of grease-proof paper. Take the butter mixture and spread over the dough, leaving a gap of around 1/2 inch along the edges. Sprinkle with the chocolate. Set to one side
Roll out the other remaining bit of dough until it is approximately the same size as the first. Place it over the top and press down gently to seal the edges.
Taking a sharp knife, cut a large triangle shape in the dough (remove any extra dough and put to one side. Don't throw it away - you can roll it out and form into bread buns). Going up both sides, cut horizontal strips about an inch thick, and in turn, take each one and gently twist (the dough is very pliable and will stretch). Some of the spirals will try to spring back, so where this happens, gently lean it against its neighbour (you will be able to move it back into place before baking).
Cover with a towel and leave to proof in a warm place for a further 30 minutes. Pre-heat the oven to 220. Egg wash the top of the tree and sprinkle with pearl sugar. Bake in the middle of the oven for about 10-12 minutes.
Leave the tree to cool on the tray then transfer to a wire rack to cool completely. If you are not using the bread right away, cover and store in the freezer, removing a couple of hours before you need it. If eating immediately, sprinkle with whatever decoration you like and serve. Enjoy!