def insert_after_node(data, node)
      Node(data).tap do |new_node|
        new_node.prev = node
        new_node.next = node.next
        if node.next
          node.next.prev = new_node
        else
          @tail = new_node
        end
        node.next = new_node
        @length += 1
      end
    end
def insert_after_node(data, node)
      Node(data).tap do |new_node|
        new_node.prev = node
        new_node.next = node.next
        if node.next
          node.next.prev = new_node
        else
          @tail = new_node
        end
        node.next = new_node
        @length += 1
      end
    end
Inserts data after first matched node.data.

 == Returns:
 Inserted node