Merge Data / Same Path ?

I have merged two data streams, but I don't know how to combine/append (?) the data further.  I would like to merge the paths with the same number of items together. 

For example: The two paths with 6 items together so I have 1 path with 12 items.

The two paths with 9 items together so there is 1 path with 18 items. And so on.