add method
Implementation
void add(Node node) {
nodes!.add(node);
if (nodes!.length == 1) {
rect = Rect.fromLTRB(node.x, node.y, node.x + node.width, node.y + node.height);
} else {
rect = Rect.fromLTRB(min(rect!.left, node.x), min(rect!.top, node.y), max(rect!.right, node.x + node.width),
max(rect!.bottom, node.y + node.height));
}
}