You can add a ToolStripMenuItem
to another ToolStripMenuItem.DropDownItems
collection.
If you don't have a reference to your ToolStripMenuItem, you can get one by key (Name Property) or Index
var itm = menustrip1.Items["Text"];
var itm = menustrip1.Items[0];
Here is the code
var menustrip1 = new System.Windows.Forms.MenuStrip();
var item = new System.Windows.Forms.ToolStripMenuItem()
{
Name = "Test",
Text = "Test"
};
var item2 = new System.Windows.Forms.ToolStripMenuItem()
{
Name = "Test",
Text = "Test"
};
item.DropDownItems.Add(item2);
menustrip1.Items.Add(item);