How can I add nested Dictionary to firebase using Swift

Currently, I am trying to store something like

Task : {Tasks1 : {"name":"","age","","over21":""}
        Tasks2 : {"name":"","age","","over21":""}
        }

How can I store an empty nested dictionary in firebase using swift? I want to store an empty dictionary(like Task) and add nested dictionaries based on the users inputs(eg Task1, Task2 etc)