treeRoot method
Implementation
Node treeRoot() {
  Node? currentNode = this;
  while (currentNode!.parentNode != null) {
    currentNode = currentNode.parentNode;
  }
  return currentNode;
}Node treeRoot() {
  Node? currentNode = this;
  while (currentNode!.parentNode != null) {
    currentNode = currentNode.parentNode;
  }
  return currentNode;
}