Expand and Collapse Button (Incremental)

Many of us have multiple levels of folders either on the left side and espically the right side. I want a button that when you hit it ONCE it expands ONE level each click. The challenge with the expand all or collapse all is it either drills down to far or not enough. We have this feature in Sage and I used it a ton, also lobbying to get it into Ediphi! My mockup below in white and black.