I believe this data structure is called Tiered vectors, and is described in: https://www.ics.uci.edu/~goodrich/pubs/wads99.pdf
I believe this data structure is called Tiered vectors, and is described in: https://www.ics.uci.edu/~goodrich/pubs/wads99.pdf
I need to read the paper, but on high-level looks indeed similar.