如果具有父id，则将项目的php数组转换为分层数组

function buildTree(array $array, $parentId = 0) {
    $tree = array();
    
    foreach ($array as $item) {
        if ($item['parent_id'] == $parentId) {
            $children = buildTree($array, $item['id']);
            if ($children) {
                $item['children'] = $children;
            }
            $tree[] = $item;
        }
    }
    
    return $tree;
}

// 示例数据
$projects = array(
    array('id' => 1, 'name' => '项目1', 'parent_id' => 0),
    array('id' => 2, 'name' => '项目2', 'parent_id' => 0),
    array('id' => 3, 'name' => '子项目1', 'parent_id' => 1),
    array('id' => 4, 'name' => '子项目2', 'parent_id' => 1),
    array('id' => 5, 'name' => '子项目3', 'parent_id' => 2),
    array('id' => 6, 'name' => '子项目4', 'parent_id' => 2),
    array('id' => 7, 'name' => '子子项目1', 'parent_id' => 3),
    array('id' => 8, 'name' => '子子项目2', 'parent_id' => 3),
);

$tree = buildTree($projects);
print_r($tree);

Array
(
    [0] => Array
        (
            [id] => 1
            [name] => 项目1
            [parent_id] => 0
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 3
                            [name] => 子项目1
                            [parent_id] => 1
                            [children] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 7
                                            [name] => 子子项目1
                                            [parent_id] => 3
                                        )

                                    [1] => Array
                                        (
                                            [id] => 8
                                            [name] => 子子项目2
                                            [parent_id] => 3
                                        )

                                )

                        )

                    [1] => Array
                        (
                            [id] => 4
                            [name] => 子项目2
                            [parent_id] => 1
                        )

                )

        )

    [1] => Array
        (
            [id] => 2
            [name] => 项目2
            [parent_id] => 0
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 5
                            [name] => 子项目3
                            [parent_id] => 2
                        )

                    [1] => Array
                        (
                            [id] => 6
                            [name] => 子项目4
                            [parent_id] => 2
                        )

                )

        )

)