private bool Contains(KdNode node, double x, double y) {
if (node == null) {
return false;
}
if (node.X.Equals(x) && node.Y.Equals(y)) {
return true;
}
if (node.Vertical && x < node.X || !node.Vertical && y < node.Y) {
return Contains(node.Left, x, y);
}
return Contains(node.Right, x, y);
}