thank you ! The glowing lights are actually just a simple emission shader with a very high strength (15k), mixed with the tree bark, the factor being some kind of noise texture

Thanks ! The key is that you need to pass both the the hit position and the direction to each new iteration. In order to avoid approximation error you'll also want to offset the new start position by the hit normal scaled down. My set up is quite messy and old, I'd rather recommend trying something else by yourself or following a tutorial online like this one for example : kzbin.info/www/bejne/iKLMdKVrYtqAnac (I actually haven't watch it but I'm pretty sure it's very similar), as it'll probably help you more than trying to understand the mess I've done but if you have question I can explain. If you want my source file : drive.google.com/drive/folders/1EzmBlX8GIN_wphjTvmekWelWe0PQDB2C?usp=sharing