Rooting, reversed. Almost [Botany]

[Externet]

Hi.

What determines a big branch off a tree cannot be rooted as a small branch can  ?  Or can it ?  Never heard of being done; every time they use a 6 inch twig instead of a 6 feet long branch.   Not being done does not mean to me that cannot be done.

Better jump to time stamp 14:20 at ---> https://www.youtube.com/watch?v=nXVCGk-P-cg

In the above video; the branch portion shown could be instead, a complete branch to the end; could it ?

 

Seen stumps sprouting several times.  Can a branch be 'attached' there instead ?

In other words... cut off a tree flush to soil.  Take a branch off the downed tree.  Graft it to a root still in the soil.  What to expect ?