For me it is the total picture - the total of nebari, trunk, branches, foliage and the way it is shaped and that gives the impression you are looking at a really old, real tree that has struggled against the elements - but then in miniature.
What I do look at most when visitings shows and exhibitions are - indeed - the branches, the way they are ramified and how the artist placed the branches, still thinking "How the hell did he do that"....