The collapsible prop allows users to create a nested, collapsible nav. Pass collapsible to any NavItem and pass that navItem any number of NavItems as children to create a collapsible nav.

The optional collapsed prop can also be used to set the default state for the collapsed nav on first render of the page. collapsed takes a boolean value that is set to true (meaning nav is collapsed) by default. Set it to false as shown here to have the nav open on first render.