Yes, you can add object parenting between two or more subjects.
To do so:

  1. Hover over the annotation and press the "hierarchy" icon.
  2. When pressed a link icon will turn on for all other compatible annotations.
  3. The selected link will become the parent annotation of the child object, and the child’s hierarchy icon will turn yellow once connected. 

You can also join parenting on selected:

  1. select all annotations in the annotations list by using Ctrl+left mouse click (Children and Parent).
  2. Press "Join Parenting on Selected". 
  3. Press the Parent to create the hierarchy.

For more information please go to Object Parenting.