How do you track nested to-dos (like subtasks for bigger tasks)?

My todos are usually subtasks. The todos should be as specific as possible. When I set my todos I also jot down how long I think it will take. This helps me insert the task into my schedule and also it helps me compare how long I think it takes vs how long the task really takes.

I use an outline method, where my list has a few larger projects I'm working on, and under those headings I list individual tasks. I use it for work and for personal life as well.
So for example:

1. Fish wall tasks
A. Make new tags
B. Cleaning tanks
a. Soak ornaments
b. Gravel vac.

I also use a tasking app called tick tick which allows me to sort my calendar into tasks within various folders.