Christmas tree cultivation species are grown as Christmas trees, although a handful of varieties stand out in popularity. In the United States, Douglas-fir, Scots pine and Fraser fir all sell well. Nordmann fir and Norway spruce sell well in the United Kingdom, the latter being popular throughout Europe. Like all conifers, Christmas trees are vulnerable to a range of pests. The final stage of cultivation, harvesting, is carried out in a number of ways; one of the more popular methods is the pick-your-own tree farm, where customers are allowed to roam the farm, select their tree, and cut it down themselves. Other farmers
WAVL tree WAVL tree In computer science, a WAVL tree or weak AVL tree is a self-balancing binary search tree. WAVL trees are named after AVL trees, another type of balanced search tree, and are closely related both to AVL trees and red–black trees, which all fall into a common framework of rank balanced trees. Like other balanced binary search trees, WAVL trees can handle insertion, deletion, and search operations in time per operation. WAVL trees are designed to combine some of the best properties of both AVL trees and red–black trees. One advantage of AVL trees over red–black trees is that