I suppose this idea would naturally occur to a certain kind of mechanically-inclined person: mount one bicycle on top of another, and have a double-decker bike. A wealth of videos shows it has occurred to more than a few.
Back in my neighborhood, circa 1962, one of our weirder characters attained celebrity–a front page spread, with photo, in our local weekly newspaper–by creating one of these tall bikes. It surprised us all. We knew him best for being the kind of person our parents ordered us to stay away from, or else. The police were very well acquainted with him. But once he started riding his double-decker bike around town, no one could keep us kids away from him.
He finally came up short when a few of us dared him to ride his bike across the ice on Tommy’s Pond. As might have been expected, halfway across, the ice gave way and down he went into some exceedingly cold water. He struggled out, somehow–the pond is only two feet deep, at the most–but that was curtains for his bike. He never resurrected it. Then he went back to stealing sheets and other items from his neighbors’ clotheslines, attaining another but less desirable kind of fame; and our parents went back to warning us off his company.
Our town was smaller then, much smaller; and its more eccentric citizens more visible.