tree_search
state = tree_search(tree, cur_start);
state = tree_search(tree, cur_start);
state = tree_search(tree, start);
state = tree_search(tree, start);
state = tree_search(tree, start);
state = tree_search(tree, start);
state = tree_search(tree, start);
state = tree_search(tree, start);
rb_node = tree_search(&tree->root, start, &prev_or_next);