okay, i've seen tons of lore errors, i'll clear stuff up for everyone
1. There are a total of three world trees in Azeroth, Nordrassil (the one in Warcraft III), Teldrassil (a newly planted one, MUCH bigger than Nordrassil, though this was corrupted and did not recieve the blessing of nature like Nordrassil did, causing it to become corrupted and some of the wildlife within it to be crazed. Darnassus is built on the top of Teldrassil.), and Vordrassil, a failed world tree which was taken down because it was discovered its roots were being corrupted by an Old God, later revealed to be Yogg-Saron. Vordrassil's remains are now the Furbolg city of Grizzlemaw.
Since I did not see this answered for the people who asked "why do we even need a world tree?", here it is.
The World Tree granted the Night Elves Immortality, though if you watch the cinematics in the end of the Night Elf Campaign in RoC Malfurion explains to Tyrande he knows a way to destroy Archimonde, though it would require the power of the World Tree and giving up their immortality. Malfurion was successful, but their immortality was lost. Even though it was lost the Night Elves still live extremely long lives to over 800 years.