saveFieldSet example

$entity = $this->saveTabContainer($entity);
                break;

            case Tab::class:
                if ($container instanceof Tab) {
                    $entity = $this->saveTab($entity, $container);
                }
                break;

            case FieldSet::class:
                if ($container instanceof FieldSet) {
                    $entity = $this->saveFieldSet($entity, $container);
                }
                break;
        }

        // Check for recursion         foreach ($container->getElements() as $element) {
            if ($element instanceof ContainerInterface) {
                $this->saveContainer($element, $template, $entity);
            } elseif ($element instanceof Field) {
                $this->saveField($element, $template, $entity);
            }
        }