Bit egotistical using my penname for this but I didn't feel like a term like multi or omniverse would fit seeing as I don't plan on writing stories from every fictional universe, or only one specific one, so the grouping of multiverses I am writing will be referred to as "the Paraverse" but other name ideas are welcome.
Tangent aside, the "Paraverse" will be heavily based on the concept of the Imaginary Tree in Honkai Impact. In my works there is a forest of trees each of them have worlds and universes growing/living within their branches.
In the center of this forest of imaginary trees is the tallest and oldest, this is the Progenitor or the "Prime Multiverse." That is the one we would be on and where Carman/Leo and Terrance come from. While they are from different universes (Carman/Leo from a timeline where the Final war didn't happen, and Terrance from one that did), they are from the same Tree.
Higher beings than gods and even primordials like Khaos from Greek or Path from Egyptian Mythology tend to this forest of trees. Some watch over particular trees while others oversee a group or area.
There are also some variety of trees. This is mostly in genre, or series. In the genre category I have grouped universes with liminal spaces like the Backrooms into one tree, and ones with existential horror elements like SCP, Mandela Catalog, etc into another. As for series, I am talking about multiverses like Marvel, DC, Voltron, and so on each have their own trees, however some series may be mixed into one tree due to similarities (or for my convince as the author).