Tree View Nodes Children Added While The Program Is Running?

I have been developing all sorts of programs and have found myself making a password safe program. While making this program I tried to use a listbox to display the passwords and such but have found that to be insecure and hard to manage and so I decided that adding a treeview to replace the listbox would probably be my best option. So in my program the user has an 'Add Entry' option and that loads a form where they enter the information they want put into the program and saved. So far I have it set up like this, They enter the user name in textbox 1, their password in textbox 2 and the website this information goes to in textbox 3. And then I have an 'Add Entry' button and when they press the button it adds the website to a node, and I'm trying to make the username a child of that node, How should I do this because I've been messing with this for about an hour and can't seem to figure anything out. Here is the code for the 'Add Entry' button if it helps:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Form3.TreeView1.Nodes.Add(TextBox3.Text)
Me.Close()
End Sub