Traverse Arvore Binaria

Question

I would like to make a function in PHP that goes through the entire binary tree, so I made this code.

function getTree($id, $count, $conn) {
if ((!isset($count)) || ($count = null)) {
    $count = 1;
}


$query = $conn->prepare("SELECT login FROM usuarios WHERE ID = :id");
$query->execute(array("id" => $id));
$rows = $query->fetchAll(PDO::FETCH_ASSOC);
if (count($rows) > 0) {
    for ($i = 0; $i < $count; $i++) {
        echo "-";
    }

    echo $rows[0]["login"]."<br />";
    $query = $conn->prepare("SELECT id FROM dados WHERE upline = :id");
    $query->execute(array("id" => $id));
    $rows = $query->fetchAll(PDO::FETCH_ASSOC);
    foreach($rows as $row) {
        $nivel++;
        getTree($row["id"], $count + 1, $conn);
    }

}

}

He takes all the people in there, perfect. But I would like him to search as the image shows, but, looking at the image below, this function behind, 1, 2, 4, 8, 16, 17, 9, 18, 19, and so on.

The function would look for the second line (numbers 2 and 3) and based on id 1; Then it would return and travel bringing Id 4 and 5, related to 2, and 6 and 6 related to 3 and so on.