How To Automatically Expand A Menu Item Using WPF And C#

Hi,

I have created a menu using code behind i.e from c#.

is there a property of menuitem, with which i can expand i particular menutiem.

following is my code:-
*****************************************************

Menu objmnu = new Menu();


MenuItem objmnu1 = new MenuItem();
objmnu1.header = "Root"
objmnu.Items.Add(objmnu1);


MenuItem objm1 = new MenuItem();
objm1.header = "Child1"
objmnu1.Items.Add(objm1);


MenuItem objm2 = new MenuItem();
objm2.header = "Child2"
objmnu1.Items.Add(objm2);


MenuItem objm21 = new MenuItem();
objm21.header = "Node1"
objm2.Items.Add(objm21);


MenuItem objm22 = new MenuItem();
objm22.header = "Node2"
objm2.Items.Add(objm22);
*****************************************************

what i want is on click of a button i want to expand "Child2" node.

i need help.

bye
Mohan Nautiyal