Ok so as Mr. David Beaulieu iinformed me there are some more cool tree diseases. And it is known under the name of A burl (British bur or burr) according to all mighty wiki. So as far as i understand its similar to previously described cancer. According to wiki, its cosed by any kind of stress to a tree,. be it human related humidity related, or most popular is insect infestations. Again according to wiki, burls are always covered with bark, even if they are underground. Ok, but enough words, lets see some pictures (all images taken from wiki here)
So be sure to go here:
its a flicker search with word burl…. so nice images :)
well thats it for now.
oh oh. some more links:
wood burls by David Beaulieu
and some famous tree, which is probably not related to burls, but still very nice.