WordPress Side Navigation with Parent Heading and Child Sub Pages - php

Question

I have the following navigational structure in WordPress:
Page
Sub Page
Child Page
Child Page
Child Page
Page
Sub Page
Child Page
Child Page
Child Page
Page
Sub Page
Child Page
Child Page
Child Page
On each Sub Page and Child Page, I want to display the following in the sidebar:
Sub Page
Child Page
Child Page
Child Page
The closest I've come to this is the following code from here:
<ul>
<?php
global $post;
$current_page_parent = ( $post->post_parent ? $post->post_parent : $post->ID );
wp_list_pages( array(
'title_li' => '',
'child_of' => $current_page_parent,
'depth' => '1' )
);
?>
</ul>
However, on Sub Pages it only shows a list of all Sub Pages (without Child Pages) and on Child Pages, it displays a list of Child Pages of that section but the parent Sub Page title is missing.
How do I modify to achieve what I'm looking for?
Thanks!

Answer 1

Yes, you are right this is not showing parent page on child or sub for that you may use following code.
<?php if ( $post->post_parent ) {
$children = wp_list_pages( array(
'title_li' => '',
'child_of' => $post->post_parent,
'echo' => 0
) );
$title = get_the_title( $post->post_parent ); } else {
$children = wp_list_pages( array(
'title_li' => '',
'child_of' => $post->ID,
'echo' => 0
) );
$title = get_the_title( $post->ID );} if ( $children ) : ?>
<h2><?php echo $title; ?></h2>
<ul>
<?php echo $children; ?>
</ul>

Answer 2

Mukesh Ram's code is working, just missing the final ENDIF
<?php if ( $post->post_parent ) {
$children = wp_list_pages( array(
'title_li' => '',
'child_of' => $post->post_parent,
'echo' => 0
) );
$title = get_the_title( $post->post_parent ); } else {
$children = wp_list_pages( array(
'title_li' => '',
'child_of' => $post->ID,
'echo' => 0
) );
$title = get_the_title( $post->ID );} if ( $children ) : ?>
<h2><?php echo $title; ?></h2>
<ul>
<?php echo $children; ?>
</ul>
<?php endif; ?>