How to set the SubMenu and SubMenu in the option can be selected？

What problem does this feature solve?

SubMenu optional

What does the proposed API look like?

<SubMenu onSelected={this.onSelected} key="sub1" title={<span><Icon type="mail" /><span>Navigation One</span></span>}>
          <Menu.Item key="1">Option 1</Menu.Item>
          <Menu.Item key="2">Option 2</Menu.Item>
          <Menu.Item key="3">Option 3</Menu.Item>
          <Menu.Item key="4">Option 4</Menu.Item>
</SubMenu>

[0xNoSignal]

Actually there is quiet a lot of use cases for this.

For example, if you sell different kind of furniture, you have

• Sideboards – Highboards – Lowboards – Sideboards
• Couches – 2-Seater – 3-Seater – L-Couch

and you obviously want to be able to select all the sideboards or all the couches and not just the deepest level

[yuribit]

@benjycui, I have a scenario similar to the one described in the comment above, should I open a new issue?