If you have tasks in your Calendar, setup up your Account in the Modern UI Mail App and it will show all of the Calendar Items in the default Calendar Live Tile and Lock Screen.
OP adds his tasks to his Calendar, so for them to show up on the Live Tile Calendar he needs to add his account to Mail, as Outlook does not have a Live Tile.
Sorry I missed that, it appeared you entered your task into your Outlook Calendar. I'm not aware of a Task Tile that will pull from Exchange. Calendar would be the way I would do it.