The leaves are weird. The guy on the video seems to think that he has invented this style. At it's basic level, it is scribbling about where the leaves might be then drawing a bit over it.
What I did learn from this is drawing from the elbow - when you want a straight-ish line that looks organic (like the tree trunk or branches). Best way to do this is to relax your hand and lead from the elbow rather than the hand or wrist.
I don't like my tree. It looks stupid.
The problem with following a tutorial is that you don't develop your own style, but I don't really think that I'm ready to start developing my own 'style'. I probably have to work out how to draw basic things like trees and people and houses first, then I can start having a style.