title_body: Collapse and Expand Table of Contents in Kindle PaperWhite
upvoted_answer: There is a right-facing black triangle (&#9654;) on each menu item that can be expanded, clicking on which the menu expands and the triangle becomes downward facing (&#9660;) which again is clickable to collapse the sub-menu.
  
  I see how easy it is to miss given the arrows are very small in size.