怎么样：

function recurse($categories, $parent = null, $level = 0)
{
    $ret = '<ul>';
    foreach($categories as $index => $category)
    {
        if($category['root'] == $parent)
        {
            $ret .= '<li><a href="#"><p class="Tier' . $level . '">' . $category['name'] . '</p></a>';
            $ret .= $this->recurse($categories, $category['id'], $level+1);
            $ret .= '</li>';
        }
    }
    return $ret . '</ul>';
}

此函数要求您首先在数据库中查询可用类别的整个列表，并假设您的根类别的值为null，但是可以根据当前模式的工作方式将该函数更改为接受-1或0。

$categories = { get from database into an multi-dimensional array };
$Tree = $this->recurse($categories);
echo $Tree;

您可以考虑执行以下操作，以防止在父级不存在任何子级时出现任何空的UL：

function recurse($categories, $parent = null, $level = 0)
{
    $ret = '<ul>';
    foreach($categories as $index => $category)
    {
        if($category['root'] == $parent)
        {
            $ret .= '<li><a href="#"><p class="Tier' . $level . '">' . $category['name'] . '</p></a>';
            $sub = $this->recurse($categories, $category['id'], $level+1);
            if($sub != '<ul></ul>')
                $ret .= $sub;
            $ret .= '</li>';
        }
    }
    return $ret . '</ul>';
}

但是，最好的解决方案是选择数据以包括一列，该列包含每个类别有多少个子类别。

select Category.*, (select count(distinct c1.id) from Category as c1 where c1.root = Category.id) as ChildCount from Category

您的功能将是：

function recurse($categories, $parent = null, $level = 0)
{
    $ret = '<ul>';
    foreach($categories as $index => $category)
    {
        if($category['root'] == $parent)
        {
            $ret .= '<li><a href="#"><p class="Tier' . $level . '">' . $category['name'] . '</p></a>';
            if($category['ChildCount'] > 0)
                $ret .= $this->recurse($categories, $category['id'], $level+1);
            $ret .= '</li>';
        }
    }
    return $ret . '</ul>';
}

希望有帮助吗？