Insertion in binary search tree using recursion in vb.net

Vb program for Insertion in binary search tree using recursion. Here problem description and other solutions.

' Include namespace system
Imports System 
'  Vb.net program for
'  Insertion in binary search tree by using recursion

Public Class TreeNode
    Public  data As Integer
    Public  left As TreeNode
    Public  right As TreeNode
    Public Sub New(ByVal data As Integer)
        Me.data = data
        Me.left = Nothing
        Me.right = Nothing
    End Sub
End Class

public Class BinarySearchTree
    Public  root As TreeNode
    Public Sub New()
        Me.root = Nothing
    End Sub
    '  Insert a node element
    Public Function  addNode(ByVal node As TreeNode, 
                             ByVal data As Integer) As TreeNode
        if (node IsNot Nothing) Then
            if (node.data >= data) Then
                '  When new element is smaller or
                '  equal to current node
                node.left = Me.addNode(node.left, data)
            Else
                '  When new element is higher to current node
                node.right = Me.addNode(node.right, data)
            End IF
            '  important to manage root node
            Return  node
        Else
            Return  New TreeNode(data)
        End IF
    End Function
    '  Display preorder
    Public Sub preorder(ByVal node As TreeNode)
        if (node IsNot Nothing) Then
            '  Display node value
            Console.Write("  " + node.data.ToString())
            '  Visit to left subtree
            Me.preorder(node.left)
            '  Visit to right subtree
            Me.preorder(node.right)
        End If
    End Sub
    Public Sub inorder(ByVal node As TreeNode)
        if (node IsNot Nothing) Then
            '  Visit to left subtree
            Me.inorder(node.left)
            '  Display node value
            Console.Write("  " + node.data.ToString())
            '  Visit to right subtree
            Me.inorder(node.right)
        End If
    End Sub
    Public Sub postorder(ByVal node As TreeNode)
        if (node IsNot Nothing) Then
            '  Visit to left subtree
            Me.postorder(node.left)
            '  Visit to right subtree
            Me.postorder(node.right)
            '  Display node value
            Console.Write("  " + node.data.ToString())
        End If
    End Sub
    Public Shared Sub Main(ByVal args As String())
        Dim tree As BinarySearchTree = New BinarySearchTree()
        '         10
        '        / \
        '       /   \
        '      4     15
        '     / \   /
        '    3   5 12
        '    -------------
        '    Build binary search tree
        tree.root = tree.addNode(tree.root, 10)
        tree.addNode(tree.root, 4)
        tree.addNode(tree.root, 3)
        tree.addNode(tree.root, 5)
        tree.addNode(tree.root, 15)
        tree.addNode(tree.root, 12)
        '  Display tree nodes
        Console.WriteLine("Preorder ")
        tree.preorder(tree.root)
        Console.WriteLine( vbLf &"Inorder ")
        tree.inorder(tree.root)
        Console.WriteLine( vbLf &"Postorder ")
        tree.postorder(tree.root)
    End Sub
End Class

Output

Preorder
  10  4  3  5  15  12
Inorder
  3  4  5  10  12  15
Postorder
  3  5  4  12  15  10