Hi, I planted a tree a few years ago ( I don't know what species it is ATM,
but it's supposed to grow small orange berries or something in fall) and it
was growing at a decent pace, but now some idiots have kicked it or
something and broke it. There is a small stump sticking out which will
hopefully start growing again, but I want to know if it's possible to save
the top part of the tree and make it grow roots again somehow. I know some
plants can do this, but I don't know if this happens with trees and if it
does, what process to take.

I have hacked off the end of the trunk so it's level as someone told me to
do, and then put it in water for a few weeks. The person who told me to do
this said roots would start growing in a few weeks, but after 3 weeks there
doesn't appear to be any sign of roots regenerating. The leaves aren't
looking that good either. Is it still possible to save this tree? Should I
plant it in soil perhaps? All help is appreciated and I hope I'm asking this
in the correct group because this is the only plant one I could find.

P.S. What is this process of roots growing from the bottom of the trunk/stem
(when there's none there) called because I couldn't find any information on
the net when searching?