Expandable menu similar to what is linked below.

Going to be redoing the site listed below. The site-map will stay the same, but it must be adapted to a wordpress theme. My main concern is finding a plug-in that will add a menu similar to how it is now. Any suggestions for this?

https://www.mycs.org/viewsubcontent.asp?sectionID=35452&subsectionID=354473&subsubsectionID=6543895