Get the function prefix_build_tree() from - https://gist.github.com/02b5611b48f1e7ce397cd191bd44a2cf - Read more at https://maheshwaghmare.com/?p=37686

nested-page-markup.php

<?php
function prefix_page_tree_markup( $page_id = 0 ) {
	$pages = prefix_get_page_tree( $page_id );

	if( empty( $pages ) ) {
		if( is_user_logged_in() ) {
			echo '<p>No Post Found!</p>';
		}
		return;
	}
	
	echo '<ul>';
	foreach( $pages as $page ) {
		echo '<li><a href="'.$page['link'].'">'. $page['post_title'] . '</a>';

		if( ! empty( $page['children'] ) ) {
			echo '<ol>';
			foreach( $page['children'] as $child_1 ) {
				echo '<li><a href="'.$child_1['link'].'">'. $child_1['post_title'] . '</a>';
	
				if( ! empty( $child_1['children'] ) ) {
					echo '<ol>';
					foreach( $child_1['children'] as $child_2 ) {

						echo '<li><a href="'.$child_2['link'].'">'. $child_2['post_title'] . '</a>';

						if( ! empty( $child_2['children'] ) ) {
							echo '<ol>';
							foreach( $child_2['children'] as $child_3 ) {
								echo '<li><a href="'.$child_3['link'].'">'. $child_3['post_title'] . '</a>';
								echo '</li>';
							}
							echo '</ol>';
						}
	
						echo '</li>';
						
					}
					echo '</ol>';
				}
	
				echo '</li>';
	
			}
			echo '</ol>';
		}
		echo '</li>';
	}
	echo '</ul>';
}