code: public function Form()
      {
          $formAction = $this->getFormActionFromRequest($this->request);
          $fields = $formAction->getFields();
          $fields->push(HiddenField::create('action', '', $formAction->getButtonName()));
  
          $form = Form::create(
              $this,
              'Form',
              $fields,
              FieldList::create(
                  FormAction::create('nestedFormSave', 'Save')
              )
          );
  
          return $form;
      }
docs: Create the nested form
  
  @return  Form