Sub Objective and Hierarchy:
This feature lets you create a sub-objective for your objective and create a hierarchical order for your OKRs.
How it works:
Step 1- After creating Top level objective, just select the expand option
Step 2- There you will see an option to Add new objective.
Step 3 - Just select the option and create new objective.
P.S. You can create sub objective for every objective by just selecting expand option and creating new objectives.
Purpose:
This feature serves the great purpose of to provide a tree view for your goals as per your organizational structure or your requirements.
Benefit:
Having all your sub objectives under your one ultimate goal helps one to focus on the bigger goals as well as micro goals to achieve it.