Add a Create Subfolder option to the menu that's presented when right clicking on a folder in the tree view. Place it after Edit Folder and before Delete. That way a user can create a subfolder on any visible folder without having to switch to that folder first. This will make it faster to build out folder structures. An option to hide the Create Folder button above the tree view would also be a nice compliment to this. It would give more vertical space for folders and you wouldn't have to scroll up to get to Create Folder button when the tree view gets really tall.