Parsing non-JSON key - lists-of-values pairs

I am trying to parsing with a logstash filter the following pattern:

[ [k1, [ v11, v12, v13 ] ], [ k2, [ v21 ] ], [k3, [ v31, v32 ] ] ]

This is a list of key value pairs with varying length, where the values are lists of varying lengths as well.
I would like to obtain an outpuyt where the keys are nested properties and the lists of values are interpreted as lists of values in elasticsearch.

I have looked around for a while but I couldn't understand how to do it with the built-in filters. It is not a JSON (no "" around strings, no {}, no : ) format so it can't be done with the json filter, while I can't figure how to do it using the kv filter.

Do you have any advice for me?
Thanks