For the meringue trees, preheat the oven to 95 °C. Separate the eggs very carefully.
Beat the egg whites with a pinch of salt until semi-stiff, then stir in half of the powdered sugar portinsweise and finish beating the mixture to a very firm and stable foam.
Cut the vanilla bean with a knife and scrape out the pulp. Mix the food coloring in the filtered lemon juice and add to the beaten egg whites with the vanilla pulp and the remaining powdered sugar, one tablespoon at a time.
Fill the beaten egg whites into a piping bag with a star-shaped nozzle and pipe small trees about 3 cm in diameter and 4 cm high onto a baking tray lined with baking paper.
Carefully decorate the meringue trees with sugar decorations and leave to dry in the oven for at least 2 hours (!).