This feature is available with Enterprise and Business plans. See Pricing plans for more details.
Groups is a feature that makes it easier for you to work within teams. Groups can hold many organizations, and each organization can contain many collaborators.
As well as creating organizations within your enterprise groups, you can also create them within your own personal group. This is ideal if you want to monitor your own personal projects outside of your enterprise’s group, or if you want a sandbox to play with.