Inserting items into the last spot on a series of branches

Hello all,

I’m trying to figure out how to insert B list items to the back of A lists. The inserted B item goes to the back of the corresponding A branch. So item 2 in B list goes to the bottom of branch 2 in A list. Any points will be appreciated, thanks!

this could be one way

if you have more items in list B than number branches in list A, you could trim list B using something like shortest list


Thank you so much!