Don't forget the hinny - a mule is only a male donkey/female horse offspring - hinny is the reciprocal and has very distinct characteristics, similar to how tigrons/ligers are distinct.
> Mules are a cross bread of donkey and horse and are effectively sterile, ergo no tree.
Not always.[1]
[1] https://horses.extension.org/is-there-a-chance-that-a-mule-m...
https://en.wikipedia.org/wiki/Mule