I agree with it likely being mulberry. COULD be elm, as elm saplings often have lots of pin knots and tiny pointy bumps. COULD even be yellow locust, which is usually pinker and not so dark, and has kind of kinky grain, but I have seen especially dense wood from medium-sized trunks have very reddish, dark heartwood.
I have never seen and handled black ash.
Either way, i agree with half-parallel-half-tapered flatbow design. When you go to shape it, cut a square or round dowel about 10 cm long from the upper corners where you side taper the limbs and find out the S.G of the wood. Then we can help you more with design.