Hi woodworkers

I've recently picked up a few tools to get into artisanal woodwork, and I want to do 1 or 2 projects that entails hollowing out natural branches.

The "perfect" outcome would be something similar to bamboo shoot, which have a narrow edge and hollow center. I'm not really expecting to be able to do this by hand with millimetric accuracy, but it gives you an idea of what I'm aiming for.

I own a high-speed rotary tool that is "technically" able to carve wood, but the bits I own atm are more of a finish toolkit. I successfully used a sanding head to carve out some wood, but I don't think it's remotely optimal for projects any bigger than what I was working on.

So all this context leads to this question: What would be the optimal tool to efficiently hollow out a branch? I can't reliably use a drill, because there's no certainty that the branches I'll work with will be remotely straight, I'm guessing that a mill file could get me some mileage but it sounds like a last resort kind of tool.