Pages work this way, so you could either use pages or create a new post type (you’d need the hierarchical => true:
function codex_custom_init() {
$labels = array(
'name' => _x('Books', 'post type general name', 'your_text_domain'),
'singular_name' => _x('Book', 'post type singular name', 'your_text_domain'),
'add_new' => _x('Add New', 'book', 'your_text_domain'),
'add_new_item' => __('Add New Book', 'your_text_domain'),
'edit_item' => __('Edit Book', 'your_text_domain'),
'new_item' => __('New Book', 'your_text_domain'),
'all_items' => __('All Books', 'your_text_domain'),
'view_item' => __('View Book', 'your_text_domain'),
'search_items' => __('Search Books', 'your_text_domain'),
'not_found' => __('No books found', 'your_text_domain'),
'not_found_in_trash' => __('No books found in Trash', 'your_text_domain'),
'parent_item_colon' => '',
'menu_name' => __('Books', 'your_text_domain')
);
$args = array(
'labels' => $labels,
'public' => true,
'publicly_queryable' => true,
'show_ui' => true,
'show_in_menu' => true,
'query_var' => true,
'rewrite' => array( 'slug' => _x( 'book', 'URL slug', 'your_text_domain' ) ),
'capability_type' => 'post',
'has_archive' => true,
'hierarchical' => true,
'menu_position' => null,
'supports' => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt', 'comments' )
);
register_post_type('book', $args);
}
add_action( 'init', 'codex_custom_init' );