Merging trees so that their items alternate

Hello everybody,

Im having a hard time applying logic using trees.

I want to merge two trees so that their items alternate.

 I am trying to make the resulting tree have the same amount of branches as the originals, only their items need to be added in a alternating way.

To visualise I have added a screencap. I want to create an interpolated curve through both sets of points. The branches of both trees are in the right order I just want the items to become 
0,1,2,3,4,5,...

instead of
0,0,1,1,2,2,...

In the grasshopper file the question is about the two trees in the purple group.

Thanks in advance!