/**
     * Internal method to remove from a subtree.
     * @param x the item to remove.
     * @param t the node that roots the tree.
     * @return the new root.
     * @throws ItemNotFoundException if x is not found.
     */
    protected BinaryNode<AnyType> remove( AnyType x, BinaryNode<AnyType> t )
    {
        if( t == null )
            throw new ItemNotFoundException( x.toString( ) );
        if( x.compareTo( t.element ) < 0 )
            t.left = remove( x, t.left );
        else if( x.compareTo( t.element ) > 0 )
            t.right = remove( x, t.right );
        else if( t.left != null && t.right != null ) // Two children
        {
            t.element = findMin( t.right ).element;
            t.right = removeMin( t.right );
        }
        else
            t = ( t.left != null ) ? t.left : t.right;
        return t;
    }