Side bar navigation between units

Hi, Could you provide some advice on how I can change the side bar of my online courses where it shows the units to be a collapsible menu? or to just improve the formatting of the side menu? See the attached image "side bar menu", this is a zoomed out view of one of my courses. Notice on the right hand side how the black side bar that lists each unit is really long and  difficult to navigate? for example, if someone wanted to skip from section 1 to to section 6 they'd have to scroll all the way to the bottom to click a unit in section 6 then back to the top to see the content? I'm wondering if it's possible to create collapsible menus on this right side bar so that the user could collapse and expand each section (there's 6 sections) so when they expand each section they could see the units within each section, rather than scrolling all the way down. Could you help me to improve this navigation on the side bar? Thanks!