The wp_list_pages() function uses get_pages(), which accepts a post_type argument-array key, so you can use that same argument array key in `wp_list_pages():

<?php
wp_list_pages( array(
    'post_type' => 'casestudy'
) );
?>

Unfortunately, it looks like the post_type value must be a string, rather than an array (that is, if I'm reading the source correctly); which means that wp_list_pages() can only handle one post-type at a time. If you need to list all in one menu, you could try concatenating them:

<?php

$pagelist = wp_list_pages( array( 
    'include' => '154, 136', 
    'title_li' => '', 
    'sort_column' => 'ID', 
    'sort_order' => 'DESC', 
    'depth' => '1'
    'echo' => false
) );

$casestudylist = wp_list_pages( array(
    'post_type' => 'casestudy'
    'title_li' => '',
    'echo' => false
) );

$concatenatedlist = $pageslist . $casestudylist;
?>

<ul>
<?php echo $concatenatedlist;
</ul>

Codex references:

• wp_list_pages()
• get_pages()

The wp_list_pages() function uses get_pages(), which accepts a post_type argument-array key, so you can use that same argument array key in `wp_list_pages():

<?php
wp_list_pages( array(
    'post_type' => 'casestudy'
) );
?>

Unfortunately, it looks like the post_type value must be a string, rather than an array (that is, if I'm reading the source correctly); which means that wp_list_pages() can only handle one post-type at a time. If you need to list all in one menu, you could try concatenating them:

<?php

$pagelist = wp_list_pages( array( 
    'include' => '154, 136', 
    'title_li' => '', 
    'sort_column' => 'ID', 
    'sort_order' => 'DESC', 
    'depth' => '1'
    'echo' => false
) );

$casestudylist = wp_list_pages( array(
    'post_type' => 'casestudy',
    'title_li' => '',
    'echo' => false
) );

$concatenatedlist = $pageslist . $casestudylist;
?>

<ul>
<?php echo $concatenatedlist;
</ul>

Codex references:

• wp_list_pages()
• get_pages()