Directory listing as tree in website

I have a webserver storing html report files. It's running both Tomcat and Apache (for what it matters).

From time to time I copy to the WEBAPP folder a sub folder that contains another 3 folders in each there is a HTML report.

I currently have a directory listing in a frame that lets me link to the reports, and see them in either the frame or a different tab.

I would like to create a tree in the index page that shows the content of the folders in an expandable form that changes dynamically according to the contents of the folder.