How to use asyncio.wait on an growing set of tasks?

In the following code, a task A is created and added to a set of tasks tasks.
I then use await asyncio.wait(tasks) to wait for the tasks to be finished.

But this does not take in consideration task B1 which is created inside task A (recursive function call).

Then the following code doesn't wait for B1 to finish: see the result below, the task B1 never finishes.

I think the reason is that when tasks is evaluated on line (**), it still has one single element.

Question: how to make await asyncio.wait(tasks) work on an evolving/growing set of tasks?

import asyncio

tasks = set()
i = 0

async def mytask(s):
    global i
    print('mytask %s starting' % s)
    await asyncio.sleep(1)
    if i < 4:    # limit number of tasks
        print('mytask %s creating new task' % s)
        i += 1
        tasks.add(asyncio.create_task(mytask('B%i' % i)))
    print('mytask %s len tasks:' % s, len(tasks))
    await asyncio.sleep(0.5)
    print('mystak %s finished' % s)

async def main():
    print('main starting')
    tasks.add(asyncio.create_task(mytask('A')))
    print('len tasks:', len(tasks))
    await asyncio.wait(tasks)            # (**)
    # await asyncio.sleep(10)
    print('main finished')

asyncio.run(main())

Result:

main starting
len tasks: 1
mytask A starting
mytask A creating new task
mytask A len tasks: 2
mytask B1 starting       # <--- mytask B1 will never complete!
mystak A finished
main finished

If we replace line (**) by await asyncio.sleep(10), of course, all tasks will complete:

main starting
len tasks: 1
mytask A starting
mytask A creating new task
mytask A len tasks: 2
mytask B1 starting
mystak A finished
mytask B1 creating new task
mytask B1 len tasks: 3
mytask B2 starting
mystak B1 finished
mytask B2 creating new task
mytask B2 len tasks: 4
mytask B3 starting
mystak B2 finished
mytask B3 creating new task
mytask B3 len tasks: 5
mytask B4 starting
mystak B3 finished
mytask B4 len tasks: 5
mystak B4 finished
main finished