Combine multiple lists at certain levels

Hello,
I’m trying to combine lists into a specific structure such that it matches the XML structure I need. Essentially, I need to join transposed lists into 1 data set, but because of the XML structure I need, the lists need to be joined at certain levels (or sublists) within the list. So basically, I need a list of lists.

I’m hoping there’s a way to do this using design script. I tested the “Add Item to End” or “List.Join” nodes, but because I have multiple lists requiring different levels, I don’t seem to get the results I desire. Here’s my test below…I know my code block is wrong, but how do I correct it to add List B and List C at different levels within the list?

This is my desired result for this example

In my other script I will be pulling parameters from families and organizing the lists the same way to get the same result, but with a total of 6 lists (some which I’ll add to the same Level within the list as the other lists - for example, if List C is at Level 1, future List D could also be at Level 1 but with different data)

Many thanks!
Michelle