This stories bullshit.
it would appear the bike dates more from the 40s than the 14s.......not to mention that the part of the tree that is close to the ground never goes "up", the growth occurs at the top of a tree, therefore the bike shouldn't have moved up above eye level if it were chained at the ground.........I would say its more likely someone figured out how to fasten two parts of a bike to a tree.......
I would believe that, if I hadn't seen carvings "climb" up the side of a tree. If somebody put their bike between two trunks from the same root system, it would grow "into" the tree and would "climb"...
Anyway, it's possible for the bike to rise. And if it is the 40s it may be from WWII rather than WWI. Who the heck knows.