Ability to to stack portfolios/ "Sub-Portfolio"

Hi,

It would be very useful if a portfolio could contain other “sub-portfolios”. We often have three or four layers, for example:
Level 1: Client
Level 2:—Area [For Example: IT]
Level 3:------Initiative [For Example: Security]
Level 4---------Projects

If in each of the “Levels 1-4”, a Sub-portfolio could be added, it would make the structuring a lot more neat. Additionally, a mix of “projects” and “portfolios” may also be helpful: For example: Maybe a small Initiative only has 1 Project - therefore no Sub-portfolio is needed - where another may have multiple projects underneath it.

Thanks,
ej