The World Trees are tallest type of trees that put their roots on a mountain range, intake magma, surpass the atmosphere and become even bigger. They grow mostly in the "outside" world but at least one of them is in the "known" world. The World Tree in the "known" world is only a sapling that has only enough nutrients to grow 1784 meters. When Gon climbed the tree to meet Ging, there was a nest which contained an unknown species of a huge bird.
According to the tour guide, climbing the tree is not forbidden but climbers have to pay a fee and sign written agreement. At the 500 meter points, climber can reach its with elevators or stairs. 500 meter point and above requires climber to climb by themselves. Every year, there are at least 3000 people try to climb the tree above the 500 meter point to the top, however, mostly 94% will fail to reach the 1000 points and force to climb down. Another 4% has to pay expensive fee for rescue operation while 1% falls to their death. As the result, only 30 people are able to climb to the top and return unharmed each year. No children under 18 years old is allowed to climb the tree beyond the 500 meter point unless they are a Hunter or have a special certificate. All climbers often being issued a special wristband to call for help in case if they stuck but they have to wait for 10 minutes to be rescued.