Thanks so much for asking about how to style lists with bullets in your email campaign. And we're sorry for any problems you're having! Just highlight the text you need to style, and select the button to add either bullets or numbers:
Tip: To indent a bullet, place your cursor at the start of the bulleted text and press the Tab key on your keyboard. Press Shift + Tab to outdent the bullet.
That's a great question! I apologize at this time being able to create a sub-list like this is not a feature we currently provide. It is however a feature request we are still collecting feedback on. In fact, I have submitted this feature request in your account to the appropriate teams. Please let us know if there is anything else we can help with in the meantime!