主题：[求助]do loop语句不需要whie?

这个do loop 语句怎么没有while或者until啊？

增加分类按钮的代码：

Dim trv As WinForm.TreeView = e.Form.Controls("TreeView1")
Dim i As Integer
trv.Select()
Do
    i = i+ 1
    Dim nm As String = "分组" & i
    If trv.Nodes.Contains(nm) = False
        Dim dr As DataRow = DataTables("授权").AddNew
        Dim nd As WinForm.TreeNode = trv.Nodes.Add(nm)
        dr("分组") = nm
        trv.SelectedNode = nd
        trv.BeginEdit
        Exit Do
    End If
Loop