Explained here [1]. We live in a pseudorandom World. So everything is deterministic if you have the same set of input parameters. That includes trees as well.

I am not talking about controllable/uncontrollable variables. That has no bearing on whether a process is deterministic in theory or not. If you can theoretically control all variables (even if you practically cannot), you have a deterministic process as you can reproduce the entire path: from input to output. LLMs are currently a black box. You have no access to the billions of parameters within the model, making it non-deterministic. The day we have tools where we can control all the billions of parameters within the model, then we can retrace the exact path taken, thereby making it deterministic.

[1]: https://news.ycombinator.com/item?id=46663052