library/library_app/views/library_menu.xml

<?xml version="1.0"?>
<odoo>

    <!-- Library App Menu -->
    <menuitem id="menu_library" name="Library" />


           <!-- Action to open the Book list -->
    <act_window id="action_library_book"
        name="Library Books"
        res_model="library.book"
        view_mode="tree,form"
    />

   <!-- Menu item to open the Book list -->
    <menuitem id="menu_library_book"
        name="Books"
        parent="menu_library"
        action="action_library_book"
    />

</odoo>