Welcome to the site!
It would help us if you could indicate, in general, where you live.
I agree with
@ShimpakuBonsai that your tree appears to be some sort of willow. If that is the case, willows naturally contain very high levels of auxin (rooting hormone) and will root in nothing but a container of water. If you are looking to take that branch and start a new bonsai from it, you could probably just prune the branch, put it in a container of warm water in the sun, and wait until you see roots - at which point you can move it into soil.
However this work is best accomplished in the late spring/early summer. If you happen to live south of the equator - you're in good shape!