About dropdownlist binding

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Please explain you question.
Are you want to add items in dropdownlist in alphabetic order or wants to add alphabets?

I guess the question is about displaying the dropdown list in alphabetic manner (sorted order).

If this is the requirement then you can apply sorting on data source...

List<string> list = .....; // logic to get the list of data to display
list.Sort((a, b) => string.Compare(a, b));
DropDown1.DataSource = list;
DropDown1.DataBind();

Hope this helps...