Wooden bicycles are not very popular but are designed mostly by artists or inventors. Steel alloys is the most common material used for the tubes of a bicycle frame, but Frames can also be made from aluminum alloys, titanium, carbon fiber, hardwood or bamboo.
A bike completely made from wood doesn't work and some metal parts have to be used to stabilize it and to handle the forces involved in cycling.
It is a nice idea to use wood for a bicycle, but to use it together with metal you get many disadvantages. Wood will never
be a serious alternative to the materials like steel etc. that are used today.
Wooden bikes can help people living in poor countries to solve their specific transportation problems as can be seen in the video below.