How to Add Space in dropdownlist Item text

Hi All I am using drop dowlist to represent some hierarchycal data like tree view.
What I want to Show as
Item1
  Item1.1
  Item1.2
  Item1.3
Item 2
  Item2.1
  Item2.2
Item3
Item4
....... so on
So when user is in hierarchy level 2 or more I  have to add some space before Item so that it can visible to end user that Item1.1 is uder Item 1.

I tried using adding " " as
ddlMyList.Items.Add(new ListItem("  Item1.1","1"));
but it render as it not showing space
I also tried as
ddlMyList.Items.Add(new ListItem("  Item1.1","1"));
But still its againg render as  Item1.1



Folloing is my code 

string name ="";
string value ="";

for (int i = 0; i < MyDataSet.Tables[0].Rows.Count; i++)
   ...