Sift together the bicarbonate of soda, ginger, flour and cinnamon and pour into a food processor. Add the butter and blend until the mixture looks like breadcrumbs. Mix in the sugar.
Lightly beat the egg and golden syrup together, add to the food processor and pulse until the mix bunches together. Tip out the dough and briefly knead until smooth. Wrap in clingfilm and leave to chill in the fridge for 15 minutes.
Preheat the oven to 180°C. Line two baking trays with greaseproof paper.
On a lightly floured surface roll out the dough to a 0.5cm thickness. Use different size star shaped biscuit cutters or a small knife to cut into different sized star shapes. Cut out a star for the top of the tree.
Bake for 12-15 minutes, or until lightly golden-brown. Leave on the tray for 10 minutes and then move to a wire rack to finish cooling.
With the biggest star at the bottom, decreasing in size, layer the stars ensuring the points sit between the gaps of the star below. Fix together using buttercream.
Add the food colouring to the buttercream, then fill a piping bag and use a leaf nozzle to pipe onto the centre of the gingerbread leaves.
Place Popping Candy Sprinkles and Fruity Cubes Sprinkles onto the ends of some of the leaves.
Cut out of the royal icing a smaller white star and attach to the last gingerbread star.