Wordpress conditional functions display specific headers

<section id="banner">

    <?php if (is_tree('23')) { ?> <!-- Custom function to call all pages under the Contact Page to show specific header graphic -->

        <img src="/wp-content/uploads/2012/05/bannerContact.jpg" alt="" />

    <?php } else { ?>

    <?php if (is_page(21) || $post->post_parent=="21") { ?> <!-- Custom function to overwrite Insurance header graphics so they do not share the header graphic from  Education -->

        <img src="/wp-content/uploads/2012/05/bannerInsurance.jpg" alt="" />

    <?php } else { ?>

    <?php if (is_tree('19')) { ?> <!-- Custom function to call all pages under the Education Page to show specific header graphic -->

        <img src="/wp-content/uploads/2012/05/bannerEdu.jpg" alt="" />

    <?php } else { ?>

        <?php the_post_thumbnail('featured-image',  980, 185, true); ?>

    <?php } ?> <?php } ?> <?php } ?>

</section><!--end of slider-->