Thanks for the new comments, guys.
LBD, thanks for performing and documenting those tests. I doubt I’d use a scroll saw enough to justify the cost and space. I do have a jigsaw that I don’t use much, so I’ll keep the inverted approach (great idea) for the next time I need to cut small parts. Mine is a barrel grip Bosch that doesn’t cut with the blade perpendicular to the base. It angles the blade forward at different angles. I’d have to take care to stop the cut a bit early and clean up the intersections by hand. It’d still be better than my coping saw.
I modeled the tree awhile back. I don’t remember it taking too long to rotate the strips. It was probably one of those Zen things where I repeated the same steps so many times I didn’t really think about it. I’ve seen jigs for installing the inserts perfectly perpendicular, but I just did it by eye. I think it helps that the entire insert fit inside the soft poplar inner dowel, and that I used a large pilot hole. It still would have been safer to apply pressure around the outer collar; I’m glad I didn’t have to learn that the hard way.
Pottz, Splint, thanks for the information about your walnut prices. My place also sells what they call calico walnut for about 15/bf, which is still more than Splint can pay locally.