Line your round cake tins with cling wrap or baking paper.
Melt the marshmallows and butter in a heatproof bowl in the microwave, stirring every 30 seconds. (Mine only took 1 minute in my microwave but it depends on each one). If you don't have a microwave you can do this in a small saucepan on medium heat, stirring continuously.
Once they are melted, add in any food colouring. I chose to add pink but you could also turn your rice bubble Christmas trees green, or any colour you want!
After you have coloured your marshmallow and butter mixture, stir in the rice bubbles. Once they are fully combined, press into the tins, making sure you get right to the edges. Make it as flat and smooth as possible
Refrigerate for 2 hours, then remove from the tin and slice them like a cake - each tin should give you eight triangle slices.
Once they are sliced, insert your wooden cocktail sticks in the bottom, like a Christmas tree trunk!
Melt your white chocolate and place it in a piping bag. Snip the end off (just a tiny bit!) and pipe the tree with a garland of white chocolate. Sprinkle with your sprinkles.
Keep in the fridge until serving.