Database design for a list of task with subtask -

i want create database keeps track of list of tasks users need , in list of tasks there subtasks , sub-subtasks , on. question how design kind of database?

example: picture of tasks , subtasks

for kind of database, should create 4 tables main task, sub task, sub-subtask , sub-sub-sub task or there better way of doing it? if users want more subtasks? should create fifth table or should restrict number of subtasks available. feel having many tables in database subtasks bad database design

so have tree of tasks. should possible add foreign key column task entity references it's parent task. nesting can deep desire , there no need subtask tables.