How to list subfolders on left of Bridge

I seem to have lost my list of folders and subfolders on the LEFT side (not the main "Content" area) of Bridge.  Now, instead of being able to scroll through my subfolders on the left (and then open one of those up to reveal a subfolder's photos in the Content area), I only have thumbnails of my FOLDERS in the Content area and have to open each one up to find a subfolder.  Does anyone know how to reset the original format?  Thanks.