Clicking on a folder's expansion triangle in the sandbox window will collapse or expand the folder's content depending whether the folder is currently collapsed or expanded.

OPTION-clicking a folder's expansion triangle will collapse or expand the folder and recusively all its sub folders. This is just like in the finder.

To collapse the whole sandbox and only show the topmost folder's content, you do this:

1. Ensure the topmost sandbox folder is expanded. If it isn't, simply click its triangle.
2. Now just OPTION-click it to recursively collapse it and all subfolders.
3. Now click it again to open the first level of the hierarchy.