Treeview problem

I am having some troble.

I can get a treeview with A, B, C.......Z
Here under each of the letters I want my Contacts Last name get under correct Letter.
For example Andersson should be under A

I have managed to do a search for the contact and getting a list back with all that includes for example A.

My problem is I want it into the treeview. How do I do that?

A
   Andersson
   Andersen
    Albertsson

B
   Bengtsson
    Berntsson

and so on

Please advice me......some code would be great

private void button1_Click(object sender, EventArgs e)
        {
            Contact cust = new Contact();
            cust.FirstName = textBox1.Text;
            cust.LastName = textBox1.Text;
            contactManager.Contacts.Add(cust);
 
 
 
            listView1.Items.Add(contactManager.Contacts[0].FirstName);
            List<Contact> searchList = new List<Contact>();
 
            //Supress repainting
            treeView1.BeginUpdate();
 
            char outstr = ('A');
            
            TreeNode node;
            for (int i = 1; i < 27; i++)
            {
                node = treeView1.Nodes.Add(Convert.ToString(outstr));
                searchList = contactManager.FindALetterSearch(outstr);
                outstr +=  (char)(+1);
            }
            //resume repainting
            treeView1.EndUpdate();
        }

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