Chicago has a long, tall history of innovation in the field of tandem tall bikes.

El Arbol will not be the first tandem tall bike. Check out this lamplighting bike from Chicago at the turn of the 20th century. Read the Full story here: 

http://www.rat-patrol.org/Archives/Eiffel.html

Or how about this family contraption, complete with treddle-powered sewing machine:

Thanks Flickr friend Whymcycles    

More recent but also notable, from Chicago Critical Mass, via Georgeaye. The photo has been viewed 4500 times on Flickr.