I am sure you have seen in these video's that many of the trees bend are first wrapped with rope? This prevents the wood fibred to break through the bark. Breaking the fibres is not too much of an issue. It becomes bad when they then break through the outer layer of active bark and sapwood. By tying everying nice and tight you stop this break out from happening. So that is part of the trick.
The second thing you see is that they twist the trunk being bend. Most species are easier to bend when twisted, where one direction is clearly easier than the other.
Third thing to realize is that they do this on young nursery stock. I would be surprised if these branches are more than 2, 3 years old. All wood is still sapwood, none had hardened. The speed at which these bends seem to be made .. Do not repeat that on old material.
Finally.. Experience. The skill with which this lady moves means she has done hundreds of these trees.