splitting sun tunnel
The longer and less direct the run,the more light you will lose to absorption. And of course the split would mean you lose light in the original location.

If you really want to do this anyway, I'd consider real optics -- half-silvered mirror, focusing lenses, front-surface mirror at far end -- but cost would be high.

A second sun-tube/skylight seems a better bet. Or solar panel driving (a) full-spectrum bulb(s), though I agree that isn't the same thing.