code: public static <T extends MutableTreeNode<T>> void removeChild(T parent, T child) {
          checkArgNotNull(parent, "parent");
          int index = parent.getChildren().indexOf(child);
          checkElementIndex(index, parent.getChildren().size());
          parent.removeChild(index);
      }
docs: Removes the given child from the given parent node.
  
  @param parent the parent node
  @param child  the child node