Create nested Custom Types

Hello!

We have a structure where the parent object has some inside objects in a list, with random quantities.

For example:

[ { children: [
    { },
    { },
    { },
  },
  { children: [
    { },
    { }
  }
]

And we want to reproduce this structure on WordPress with MetaBox.
We need the inside objects of the children to be visible, and Relationships does not help us cause only the ID of the list of objects are referenced.

It would be awesome if we had some Groups on our Custom Types that we could add more if that was the case.

Is there any options that can help us with our problem?

Thanks in advance.