So you have seen in the photos what it looks like, the same method could be used to fit in any shape you like, but some are structurally better than others. The shape I used was based on the size of a scrap of teak I had left over from some other projects. Contrasting coloured wood is interesting, and makes it look like deliberate fun rather than a botched job.
The more complicated and large you make your shape the harder it will be to get it fitting tightly, without a gappy joint. I found this one quite a challenge.Tools used in this method
Router (with flush trim cutter bit - the bearing on top type)
Jigsaw, coping saw, and/or bandsaw
Safety equipment (goggles, ear defenders, dust mask, dust sniper
Your choice of Wood glue
2 part epoxy and some saved wood dust (useful if you expect to have some small gaps in you joints - you should expect this!)