Public Class myTreeNode
    Inherits TreeNode
    Protected _Window As Window
    Public Enum Window As Byte
        Window1 = 0
        Window2 = 1
        ' .usw
    End Enum
    Public Property CurrentWindow() As Window
        Get
            Return Me._Window
        End Get
        Set(ByVal Value As Window)
            Me._Window = Value
        End Set
    End Property
    Public Sub New(ByVal Text As String, ByVal CurrentWindow As Window)
        MyBase.New(Text)
        Me.CurrentWindow = CurrentWindow
    End Sub
End Class

        Dim tn1 As New myTreeNode("Window1", myTreeNode.Window.Window1)
        Dim tn2 As New myTreeNode("Window1", myTreeNode.Window.Window1)
        Dim tn3 As New myTreeNode("Window1", myTreeNode.Window.Window1)
        tn1.Nodes.Add(New myTreeNode("Window2", myTreeNode.Window.Window2))
        tn2.Nodes.Add(New myTreeNode("Window2", myTreeNode.Window.Window2))
        tn3.Nodes.Add(New myTreeNode("Window2", myTreeNode.Window.Window2))
        Me.TreeView1.Nodes.Add(tn1)
        Me.TreeView1.Nodes.Add(tn2)
        Me.TreeView1.Nodes.Add(tn3)

Private Sub TreeView1_DoubleClick(ByVal sender As Object, ByVal e As _
  System.EventArgs) Handles TreeView1.DoubleClick
        Dim tn As myTreeNode = DirectCast(Me.TreeView1.SelectedNode, myTreeNode)
        Select Case tn.CurrentWindow
            Case myTreeNode.Window.Window1
                Dim f As Form1 = New Form1
                f.Show()
            Case myTreeNode.Window.Window2
                Dim f As Form2 = New Form2
                f.Show()
        End Select
    End Sub

Dim tn As New TreeNode("Test")
tn.Tag = "Window1"
' ...