Help with creating commenting system using PHP, jQuery and AJAX

Question

I am working on creating a comment system for an events plugin I am working on. I've got the main comments working fine with them saving to the database and displaying on the page. What I need help with now is displaying a form for replies when Reply is clicked below each message, then displaying the replies with the main comments. One issue I have is that I am on an older version of MySQL so I can't use a recursive query. Any help is appreciated. My code I have is below.

Form

<form action="<?php echo site_url() ?>/wp-admin/admin-ajax.php" method="POST" id="commentform" class="commentform">
    <textarea name="comment" id="comment" class="commentbox" rows="5" cols="120" required></textarea><br />
    <input type="hidden" name="eventid" id="eventid" value="<?php echo $id; ?>" />
    <input type="hidden" name="userid" id="userid" value="<?php echo $userid; ?>" />
    <input type="hidden" name="action" value="commentform">
    <button class="commentbtn">Add Comment</button>
</form>

jQuery/AJAX

jQuery(function ($) {
    $('.commentform').submit(function () {
        event.preventDefault();
        var commentform = $('.commentform');
        $.ajax({
            url: commentform.attr('action'),
            data: commentform.serialize(), // form data
            type: commentform.attr('method'), // POST
            beforeSend: function (xhr) {
                commentform.find('button').text('Processing...');
            },
            success: function (data) {
                commentform.find('button').text('Add Comment');
                $(".commentform")[0].reset();
                $('#response').html(data); // insert data
            }
        });
        return false;
    }); 
});

PHP Function

add_action('wp_ajax_commentform', 'comment_submit');
add_action('wp_ajax_nopriv_commentform', 'comment_submit');
function comment_submit() {
    global $wpdb;
    date_default_timezone_set("America/New_York");
    $date = date('Y-m-d H:i:s');
    $inserttable = $wpdb->prefix . "event_comments";
    $eventid = $_POST["eventid"];
    $userid = $_POST["userid"];
    $comment = $_POST["comment"];

    $data = array(
        'eventid' => $eventid,
        'userid' => $userid,
        'content' => $comment,
        'datesaved' => $date,
    );

    $wpdb->insert($inserttable, $data);
}

Display Comments

$commentctr = $wpdb->get_var("SELECT count(*) FROM " . $wpdb->prefix . "cmc_communitybb_event_comments where eventid=$eventid");

echo "<h2>Comments</h2>";
echo "<h3>$commentctr Total Comments</h3>";

$commentsql = $wpdb->get_results("SELECT comm.id as id, comm.eventid as eventid, comm.userid as userid, comm.content as comment, comm.datesaved as date, users.meta_value as fname, users2.meta_value as lname
                                FROM " . $wpdb->prefix . "event_comments as comm
                                inner join " . $wpdb->prefix . "usermeta as users on comm.userid = users.user_id and users.meta_key = 'first_name'
                                inner join " . $wpdb->prefix . "usermeta as users2 on comm.userid = users2.user_id and users2.meta_key = 'last_name'
                                where comm.eventid=$eventid and comm.parentid is null order by comm.datesaved asc");

foreach ($commentsql as $comment) {
    $commid = $comment->id;
    $date = date_create($comment->date);
    $fordate = date_format($date, "m/d/Y");
    $fortime = date_format($date, "g:i a");
    ?>
    <div id="commentdiv<?php echo $commid; ?>" class="commentdiv">
        <b>Comment by: </b><?php echo $comment->fname . " " . $comment->lname; ?><br />
        <b>Date/Time: </b><?php echo $fordate . " - " . $fortime; ?><br />
        <?php  echo $comment->comment . "<br>"; ?>
        <a href="javascript:void(0);" id="replylink<?php echo $commid; ?>" class="replylink" onclick="showreplybox(<?php echo $commid; ?>)">REPLY</a>
    </div>
    <hr class="commenthr" />
    <?php
}