is there a way to define which tab is inside another like in a hierachiecal editor ?
Unfortunately no as nesting is automatically done under the Profile tab and only for non-plugin tabs.
What you can try however is use substitutions in delimiter fields to render tabs. You could then use your own HTML to format them how you please. I'm not sure about the details of putting them in tabs though, but you can render a tab with the below substitution.
[cb:usertab tab="TAB_ID_HERE" /]