public ColumnNode addChildIfNotExist(@NotNull String name) {
      if (children.containsKey(name)) {
        return children.get(name);
      }
      else {
        ColumnNode newNode = new ColumnNode();
        children = children.plus(name, newNode);
        return newNode;
      }
    }
public ColumnNode addChildIfNotExist(@NotNull String name)