You can't have nested or multiple levels within one checklist in Trello.
But you can add multiple checklists - so if you had three separate main tasks, with three sub-tasks below each, I'd just add three checklists.
As you complete the sub-tasks, the first level will show a progression bar of how far through each task you are and then complete once done.
It's not quite the same - as you can't have more sub-levels or mark a main task "Done" without all sub-tasks being done, but it's one option :)
Hello Community! My name is Brittany Joiner and I am a Trello enthusiast and Atlassian Community Leader. I'll be sharing with you a series of videos with my top tips on how to best use Trello...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events