Generate Nav In WordPress

Hi

i am currently developing a custom theme

i need to generate menu with submenu

By default wordpress provides me result like below

<ul id="side-menu" role="navigation" class="main-menu nav">

	<li class="selected" id="menu-item-485">
		<p> <a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/">Home</a> </p>
	</li>

	<li class="parent menu-item" id="menu-item-486">
		<p> <a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/about-us/">About Us</a> </p>

		<div>
			<ul id="side-menu" class="sub-menu-new">
				<li class="menu-item" id="menu-item-488">
					<p><a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/about-us/values/">Values</a></p>
				</li>
				<li class="menu-item" id="menu-item-489">
					<p><a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/about-us/vision-mission/">Vision & Mission</a></p>
				</li>
				<li class="menu-item" id="menu-item-487">
					<p><a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/about-us/quality/">Quality</a></p>
				</li>
			</ul>
		</div>
	</li>
 </ul>

I want the sub menu to come out from main ul

i need to exact result as below

<ul id="side-menu" role="navigation" class="main-menu nav">
	<li class="selected" id="menu-item-485">
		<p> <a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/">Home</a> </p>
	</li>

	<li class="parent menu-item" id="menu-item-486" data-submenuid="about">
		<p> <a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/about-us/">About Us</a> </p>
 	</li>
 </ul>

<ul data-submenuid="about" id="side-menu" class="sub-menu-new">
	<li class="menu-item" id="menu-item-488">
		<p><a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/about-us/values/">Values</a></p>
	</li>
	<li class="menu-item" id="menu-item-489">
		<p><a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/about-us/vision-mission/">Vision & Mission</a></p>
	</li>
	<li class="menu-item" id="menu-item-487">
		<p><a href="https://10.0.1.46/iir/sites/icegen/wordpress/IIR_icegen/about-us/quality/">Quality</a></p>
	</li>
</ul>

And i tried using the below php class in wordpress but the result is failure

class menu_default_walker extends Walker_Nav_Menu
{

	function start_lvl(&$output, $depth){
		$output .= '<div><ul class="sub-menu-new" id="side-menu">';
	}

	function display_element($element, &$children_elements, $max_depth, $depth=0, $args, &$output){
		$id_field = $this->db_fields['id'];
		if ( is_object( $args[0] ) ) {
			$args[0]->has_children = ! empty( $children_elements[$element->$id_field] );
		}
		return parent::display_element( $element, $children_elements, $max_depth, $depth, $args, $output );
	}

	function start_el(&$output, $item, $depth, $args) {
		global $wp_query;
		global $rb_submenus;

		$indent = ( $depth ) ? str_repeat( "\t", $depth ) : '';

		$new_output = '';
		$open_class = '';
		$depth_class = ($args->has_children ? 'parent ' : '');

		$class_names = $value = '';
		$classes = empty($item->classes) ? array() : (array) $item->classes;

		$current_indicators = array('current-menu-item','current-menu-parent','current_page_item','current_page_parent');

		$newClasses = array();
		foreach($classes as $el)
			if(in_array($el,$current_indicators))
			array_push($newClasses,$el);

		$class_names = join(' ',apply_filters('nav_menu_css_class',array_filter($newClasses),$item));

		if(strpos($class_names, 'current-menu-parent') > 0 || strpos($class_names, 'current_page_parent') > 0) {
			$class_names = ' class="' . $depth_class . $open_class . 'opened"';
		} else if($class_names != '') {
			$class_names = ' class="' . $depth_class . $open_class . 'selected"';
		} else if($class_names == '') {
			$class_names = ' class="' . $depth_class . $open_class . 'menu-item"';
		}

		if ( !get_post_meta( $item->object_id , '_members_only' , true ) || is_user_logged_in() ) {
			$output .= $indent . '<li id="menu-item-'. $item->ID . '"' . $class_names . '>';
		}

		$attributes  = ! empty( $item->attr_title ) ? ' title="'  . esc_attr( $item->attr_title ) .'"' : '';
		$attributes .= ! empty( $item->target )     ? ' target="' . esc_attr( $item->target     ) .'"' : '';
		$attributes .= ! empty( $item->xfn )        ? ' rel="'    . esc_attr( $item->xfn        ) .'"' : '';
		if($item->object != 'portfolio_category' && $item->object != 'gallery_category')
			$attributes .= ! empty( $item->url )        ? ' href="'   . esc_attr( $item->url        ) .'"' : '';
		else
			$attributes .= ' href="#"';

		$portfolio_count;
		$gallery_count;

		if($item->object == 'portfolio_category'){
			$terms = get_terms('portfolio_category', array('include' => $item->object_id));
			$portfolio_count = $terms[0]->count;
			$attributes .= ' data-category="true" data-filter="' . $terms[0]->slug .'"';
		}

		if($item->object == 'gallery_category'){
			$terms = get_terms('gallery_category', array('include' => $item->object_id));
			$gallery_count = $terms[0]->count;
			$attributes .= ' data-category="true" data-filter="' . $terms[0]->slug .'"';
		}

		if($item->attr_title == 'allportfolio' || $item->attr_title == 'allgallery'){
			$attributes .= ' data-all="true" data-filter="*"';
		}

		$item_output = $args->before;
		$item_output .= '<p><a'. $attributes .'>';
		$item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
		$item_output .= ($item->object == 'category' ? ' ('. get_category($item->object_id)->count . ')' : '');
		$item_output .= ($item->object == 'portfolio_category' ? ' ('. $portfolio_count . ')' : '');
		$item_output .= ($item->object == 'gallery_category' ? ' ('. $gallery_count . ')' : '');
		$item_output .= ($item->attr_title == 'allblog' ? ' ('. wp_count_posts()->publish . ')' : '');
		$item_output .= ($item->attr_title == 'allportfolio' ? ' ('. wp_count_posts('portfolio')->publish . ')' : '');
		$item_output .= ($item->attr_title == 'allgallery' ? ' ('. wp_count_posts('gallery')->publish . ')' : '');
		$item_output .= '</a></p>';
		$item_output .= $args->after;

		if ( !get_post_meta( $item->object_id, '_members_only' , true ) || is_user_logged_in() ) {
			$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
		}

		$output .= $new_output;

	}

	function end_el(&$output, $item, $depth) {
		if ( !get_post_meta( $item->object_id, '_members_only' , true ) || is_user_logged_in() ) {
			$output .= "</li>\n";
		}
	}

	function end_lvl(&$output, $depth) {

		$output .= "</ul></div>\n";

	}

}