How to add sub menu items in contextmenustrip using C#4.0?

To add an item, you would call

myContextMenuStrip.Items.Add("Item title", null, myClickHandler);

To add a sub-menu, you take an existing item and do the same to it:

(myContextMenuStrip.Items[0] as ToolStripMenuItem).DropDownItems.Add(...)

Define your menu strip and items

ContextMenuStrip menu = new ContextMenuStrip();
ToolStripMenuItem item, submenu;

Create new item.

submenu = new ToolStripMenuItem();
submenu.Text = "Sub-menu 1";

At this time your new item is just like others. Now create several new items and add them to submenu:

item = new ToolStripMenuItem();
item.Text = "Sub-item 1";
submenu.DropDownItems.Add(item);

item = new ToolStripMenuItem();
item.Text = "Sub-item 2";
submenu.DropDownItems.Add(item);

At last add sub-menu to your main ContextMenuStrip

menu.Items.Add(submenu);