static void Scroll(Tree tree, int x, int y) {
	TreeItem item = tree.getItem(new Point(x, y));
	if (item == null) return;
	Rectangle area = tree.getClientArea();
	int headerHeight = tree.getHeaderHeight();
	int itemHeight= tree.getItemHeight();
	TreeItem nextItem = null;
	if (y < area.y + headerHeight + 2 * itemHeight) {
		nextItem = PreviousItem(tree, item);
	}
	if (y > area.y + area.height - 2 * itemHeight) {
		nextItem = NextItem(tree, item);
	}
	if (nextItem != null) tree.showItem(nextItem);
}