动态下拉列表与PHP

Question

使用PHP我制作了这样的数组，我将显示动态下拉列表菜单。

这是PHP数组示例：

Array
(
    [0] => Array
        (
            [id] => 1
            [id_subpage] => 0
            [alias] => test
            [title] => Test
        )

    [1] => Array
        (
            [id] => 2
            [id_subpage] => 1
            [alias] => test_2
            [title] => Test 2
        )

    [2] => Array
        (
            [id] => 3
            [id_subpage] => 1
            [alias] => test_3
            [title] => Test 3
        )

    [3] => Array
        (
            [id] => 4
            [id_subpage] => 3
            [alias] => test_4
            [title] => Test 4
        )
    [4] => Array
        (
            [id] => 5
            [id_subpage] => 3
            [alias] => test_5
            [title] => Test 5
        )
    [5] => Array
        (
            [id] => 6
            [id_subpage] => 5
            [alias] => test_6
            [title] => Test 6
        )
    [6] => Array
        (
            [id] => 7
            [id_subpage] => 0
            [alias] => test_7
            [title] => Test 7
        )   
)

...这是下拉列表菜单的示例：

<ul>
    <li class="dropdown-submenu">
        <a class="dropdown-toggle" data-toggle="dropdown" data-target="test" href="test">Test</a>

        <ul class="dropdown-menu">
            <li><a href="test_2">Test 2</a></li>

            <li class="dropdown-submenu">
                <a href="test_3">Test 3 <i class="fa fa-angle-right"></i></a>
                <ul class="dropdown-menu" role="menu">
                    <li class="dropdown-submenu"><a href="test_4">Test 4</a></li>
                    <li class="dropdown-submenu">
                        <a class="dropdown-toggle" data-toggle="dropdown" data-target="test_5" href="test_5">
                            Test 5
                            <i class="fa fa-angle-right"></i>
                        </a>
                        <ul class="dropdown-menu">
                            <li class="dropdown-submenu"><a href="test_6">Test 6</a></li>
                        </ul>
                    </li>
                </ul>
            </li>
        </ul>
    </li>
    <li class="dropdown-submenu"><a href="test_7">Test 7</a></li>
</ul>

任何人都可以帮我解决这个问题吗？谢谢，Daniel J！

修改

这是我的例子，但没有正确显示：

function createTree($menu, $currentParent, $currLevel = 0, $prevLevel = 0) {
    foreach ($menu as $nav) {
        $subpageID = $nav['id_subpage'];

        if ($currentParent == $subpageID) {
            $navID      = $nav['id'];
            $navTitle   = $nav['title'];
            $navAlias   = $nav['alias'];

            if ($currLevel > $prevLevel) echo "<ul class='dropdown-menu'>";

            if ($currLevel == $prevLevel) echo "</li>";
            ?>

            <li><a href="<?= url($navAlias) ?>"><?= $navTitle ?></a>

            <?php
            if ($currLevel > $prevLevel) $prevLevel = $currLevel;

            $currLevel++;
            createTree($menu, $navID, $currLevel, $prevLevel);
            $currLevel--;
        }
    }

    if ($currLevel == $prevLevel) echo "</li></ul>";
}

createTree($menu, 0)

变量$ menu是顶部的数组...