If you want only a submit button, then it's only one form (this is how HTML forms work).
If I understood right your request, here is a suggestion:
- use javascript on a button on the page, to create more and more tasks, with an incrementing parameter
- the submit button should point to a controller's method which creates them all, identifying them by that incrementing parameter
Also, you could create the tasks using AJAX, but this means they will go to the database right away.