$array = [

    ['id' => , 'pid' => , 'name' => '这是主类'],

    ['id' => , 'pid' => , 'name' => '这是主类'],

    ['id' => , 'pid' => , 'name' => '父级为1子类'],

    ['id' => , 'pid' => , 'name' => '父级为2子类'],

    ['id' => , 'pid' => , 'name' => '父级为3子类'],

];

function tree($array, $pid)

{

    $tree = array();

    foreach ($array as $key => $value) {

        if ($value['pid'] == $pid) {

            $value['child'] = tree($array, $value['id']);

            if (!$value['child']) {

                unset($value['child']);

            }

            $tree[] = $value;

        }

    }

    return $tree;

}

echo "<pre>" . print_r(tree($array, ), ) . "</pre>";

function generateTree($rows, $id = 'id', $pid = 'pid')

{

    $items = array();

    foreach ($rows as $row) {

        $items[$row[$id]] = $row;

    }

    foreach ($items as $item) {

        $items[$item[$pid]]['son'][$item[$id]] = &$items[$item[$id]];

    }

    return isset($items[]['son']) ? $items[]['son'] : array();

}

echo "<pre>" . print_r(generateTree($array), ) . "</pre>";