Dropdown Menu code For Functions.php

// add menu support and fallback menu if menu doesn't exist
    add_action('init', 'wpj_register_menu');
    function wpj_register_menu() {
        if (function_exists('register_nav_menu')) {
            register_nav_menu( 'wpj-main-menu', __( 'Main Menu', 'brightpage' ) );
        }
    }
// For using  <UL> if we use id or class like <ul id=”dropmenu” class=””>
    function wpj_default_menu() {
        echo '<ul id="dropmenu">';
        if ('page' != get_option('show_on_front')) {
            echo '<li><a href="'. home_url() . '/">Home</a></li>';
        }
        wp_list_pages('title_li=');
        echo '</ul>';
    }