Function? backpropObserver;

  Node(
      {this.gameState,
      this.parent,
      this.move,
      this.visits = 0,
      this.depth = 0,
      this.draws = 0,
      root,
      this.c = 1.41421356237 // square root of 2
      })
      : initialState = gameState {

  Node({
    this.gameState,
    this.parent,
    this.move,
    this.visits = 0,
    this.depth = 0,
    this.draws = 0,
    root,
    this.c = 1.41421356237,
    this.backpropObserver, // square root of 2
  }) : initialState = gameState {

          backpropObserver: backpropObserver,

    Node<MoveType, PlayerType?>? rootNode = this;
    int maxDepth = this.depth;
    if (backpropObserver != null) {
      while (rootNode!.parent != null) {
        rootNode = rootNode.parent;
      }
      backpropObserver!(winner, rootNode, currentNode);
    }

  Function? backpropObserver;

  MCTS({this.gameState});

  MCTS({this.gameState, this.backpropObserver});

      rootNode = Node(gameState: gameState, parent: null, move: null, c: c);

      rootNode = Node(
          gameState: gameState,
          parent: null,
          move: null,
          c: c,
          backpropObserver: backpropObserver);