.. seealso:: :ref:`filter-menu_trail`, :ref:`filter-menu_flat`
Get the subtree of an id in a menu (if any).
Returns the subtree of the filter value. Useful for showing a part of a menu when browsing sub-pages.
If the given id is not found inside the menu, it returns
undefined.
If no argument is given, it takes menu from the resource with the name
main_menu.