Facets of multiple levels under a parent facet are known as hierarchical facets. Hierarchical facets allow faster navigation through facet submenus and breadcrumbs when navigating through the available options. Facets with children can be indicated by an arrow to indicate they have children that become visible when the arrow is selected. Selecting a child facet after expanding the facet menu allows the user to bypass the options between the top page and their choice.
Hierarchical facets are split according to the delimiter set in the Apply Rules query pipeline stage.
For more information, see How to Use Hierarchical Facets.