如何在SQL二进制树中选择正确的节点？

I am building a simple web page with a 20 questions style game. The first question is presented and the user answers yes or no get to the next question. I am unsure on how to point to the next required node with my query.

I have radio buttons for selecting the answer and a submit button. I presume I need to hand over something with the radio buttons with $_GET, but I am really struggling. I am assuming that I need a way to know which node the user is on to the find the correct answer node.

<form action="play.php" method="GET">
    <input type="submit" name="start" value="start game">
</form>
<?php
$query="SELECT `message`, `parentID`,`answerYesID`, `answerNoID`, `nodeID` FROM `creature`";
$where="";
$current=1;
function output($query, $where, $dbconn) {
    $result=mysqli_query($dbconn, $query.$where);
    while($row=mysqli_fetch_assoc($result)) {
        echo("<tr><td>{$row['message']}</td></tr><br>");
        echo "</table>";
    }
}

echo '<form action="play.php" method="GET">
        <input type="radio" name="answer" value ="`answerYesID`">yes
        <input type="radio" name="answer" value="`answerNoID`">no
        <input type="submit" name="submit" value="submit">
    </form>';
if(isset($_GET['start'])) {
    $where="WHERE `parentID` is NULL";
    output($query, $where, $dbconn);
}
if(isset($_GET['submit']) && $_GET['answer'] == "answerYesID") {
    $where="WHERE `nodeID` = ".$_GET['answer'];
    output($query, $where, $dbconn);
}
?>
</body>
</html>

you can give a Question ID to each question and get data according to this Question ID
Make ID column an auto_increment
get the id using GET method and the for next button just increment by one

$next=$_GET['id']+1;

and make sure that this number doesn't exceed 20(number of Question)

$next%=20;

now action atribute for for would be

action="play.php?id=<?php echo $next;?>"