Hi, As a user in a organization that mainly uses windows: many changes looks nice and plausible but especially 10 would be a regression. Slash by itself never indicates to the user that an action is possible when clicking on it.
As alternative to 10:
How about removing slash as the separator to the right pointing version of the current arrow and when clicking on it and opening the tree on that position it switches to the current arrow (to bottom).
I think this would improve the design (only one symbol as separator and tree opener) and still be very intuitive.