Find kth smallest element in BST vb.net

Vb program for Find kth smallest element in BST. Here mentioned other language solution.

' Include namespace system
Imports System 
'  Vb.net program for
'  K’th smallest element in Binary Search Tree
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
    Private counter As Integer
    Private element As TreeNode
    Public Sub New()
        Me.root = Nothing
    End Sub
    '  Insert a node element
    Public Function  insert(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.insert(node.left, data)
            Else
                '  When new element is higher to current node
                node.right = Me.insert(node.right, data)
            End IF
            '  Important to manage new node
            Return  node
        Else
            Return  New TreeNode(data)
        End IF
    End Function
    '  Find the kth smallest node in BST
    Public Sub findKthSmallest(ByVal node As TreeNode, 
                               ByVal k As Integer)
        if (node IsNot Nothing) Then
            '  Visit left subtree
            Me.findKthSmallest(node.left, k)
            if (Me.counter = k) Then
                '  Stop recursion
                Return
            End If
            if (Me.element  Is  Nothing OrElse 
                Me.element.data < node.data) Then
                '  Modified counter variable by one
                Me.counter += 1
                '  Collect possible result
                Me.element = node
            End If
            '  Visit right subtree
            Me.findKthSmallest(node.right, k)
        End If
    End Sub
    Public Sub printKthSsmallest(ByVal k As Integer)
        if (k <= 0) Then
            '  When given k is not valid positive values
            Console.WriteLine("Invalid node position " + k.ToString())
        ElseIf (Me.root  Is  Nothing) Then
            '  When BST are no have elements
            Console.WriteLine("Empty Binary Search Tree")
        Else
            '  Reset values
            Me.counter = 0
            Me.element = Nothing
            '  Find result
            Me.findKthSmallest(Me.root, k)
            if (Me.counter < k) Then
                '  If In case given kth smallest node are
                '  Not exist in binary search tree, then
                Console.WriteLine("Given " + k.ToString() + 
                                  " smallest node are not exist " + 
                                  Me.counter.ToString())
            Else
                Console.WriteLine("[" + k.ToString() + 
                                  "] smallest node : " + 
                                  Me.element.data.ToString())
            End IF
        End IF
    End Sub
    '  Handle request to add new node
    Public Sub addNode(ByVal key As Integer)
        Me.root = Me.insert(Me.root, key)
    End Sub
    Public Shared Sub Main(ByVal args As String())
        Dim tree As BinarySearchTree = New BinarySearchTree()
        '    Make Tree
        '    ----------
        '        7
        '       / \ 
        '      /   \
        '     4     9
        '    / \   / \
        '   3   5 8   10
        '      /    
        '     4     
        '  Add node
        tree.addNode(7)
        tree.addNode(4)
        tree.addNode(3)
        tree.addNode(5)
        tree.addNode(9)
        tree.addNode(8)
        tree.addNode(10)
        tree.addNode(4)
        '  Testing
        tree.printKthSsmallest(6)
        tree.printKthSsmallest(4)
        tree.printKthSsmallest(3)
    End Sub
End Class

Output

[6] smallest node : 9
[4] smallest node : 7
[3] smallest node : 5