Just to share a couple of experiment. I have tried the following in a playground:
b := RTMondrian new.
b shape rectangle
if: [ :aFile | aFile path basename beginsWith: '.' ] color: Color red.
b nodes: FileLocator documents allChildren.
b edges connectFrom: #parent.
normalizeSize: #size using: #sqrt.
b layout tree.
It shows a tree of the file system. Thanks to GT, simply clicking on a file may show you the content and other things.
You can also use the cluster layout:
I have tried this on OS X, since the pointed folder is ~/Documents.