怎么用vb建立二叉树，并实现先．中．后序遍历和线索化？

'二叉树的结点类
Option Explicit
Private mNodeValue As String '结点值
Private mLeftNode As clsBiTreeNode '左结点
Private mRightNode As clsBiTreeNode '右结点

'得到结点的值
Public Property Get NodeValue() As String
NodeValue = mNodeValue
End Property

'设置结点的值
Public Property Let NodeValue(ByVal pNodeValue As String)
mNodeValue = pNodeValue
End Property

'得到左结点
Public Property Get LeftNode() As clsBiTreeNode
Set LeftNode = mLeftNode
End Property

'设置左结点
Public Property Let LeftNode(ByVal pLeftNode As clsBiTreeNode)
Set mLeftNode = pLeftNode
End Property

'得到右结点
Public Property Get RightNode() As clsBiTreeNode
Set RightNode = mRightNode
End Property

'设置右结点
Public Property Let RightNode(ByVal pRightNode As clsBiTreeNode)
Set mRightNode = pRightNode
End Property