Dim Node1 as new Treenode("....")
Dim Node2 as new Treenode("....")
Dim Node3 as new Treenode("....")
.. usw
If Col.Contains(Node1) then
 ' DEIN  CODE
Endif

 Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As _
   System.EventArgs) Handles Button4.Click
        Dim node As String = "Node4"
        If TreeNodeSearch.SearchTreeNode(node, _
          TreeNodeSearch.NodeSearch.ByText, Me.TreeView1) Then
            MsgBox("Knoten schon vorhanden [node]!")
        End If
    End Sub
Class TreeNodeSearch
    Public Enum NodeSearch As Integer
        ByText = 0
        ByPath = 1
    End Enum
    Public Shared Function SearchTreeNode(ByVal Search As String, ByVal _
      SearchBy As NodeSearch, ByVal Tv As TreeView) As Boolean
        For Each tn As TreeNode In Tv.Nodes
            Return SearchTreeNode_Sub(Search, SearchBy, tn)
        Next
        Return False
    End Function
    Private Shared Function SearchTreeNode_Sub(ByVal Search As String, ByVal _
      SearchBy As NodeSearch, ByVal Tn As TreeNode) As Boolean
        If SearchBy = NodeSearch.ByText Then
            If Tn.Text = Search Then Return True
        ElseIf SearchBy = NodeSearch.ByPath Then
            If Tn.FullPath = Search Then Return True
        End If
        For Each tn_ As TreeNode In Tn.Nodes
            Return SearchTreeNode_Sub(Search, SearchBy, tn_)
        Next
        Return False
    End Function
End Class