The furo theme (with its default setting) has two side bars. The left side bar contains the contents tree for the web pages. The right side bar contains the contents tree for each individual page. This is a very nice feature because headings within a web page do not affect the overall contents tree. This facilitates moving a sub tree to a different location in the web page contents tree (in the spirit of incremental iterative development).
Are there other themes that enable one to see these two trees separately ?