请高手帮忙看一下代码！该如何解决

Imports System.Data.OleDb
Public Class Form1
    Dim data1 As New dataDataSet 'dataDataSet通过数据添加的access2003数据库
    Dim reader As DataTableReader
    Dim datarow As DataRow
    Dim con As New OleDb.OleDbConnection
    Dim i, j As Integer
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim sqlstr As String = "select 所在科室 from jbxx group by 所在科室 having count(*)>1"
        Dim datatab As DataTableReader
        datatab = conn(sqlstr)
        Dim nod(6) As TreeNode
        Dim i As Integer
        i = 0
        While datatab.Read()
            i = 1 + i
            nod(i) = New TreeNode
            nod(i) = TreeView1.Nodes.Add(datatab.GetString(0).ToString)
        End While
        datatab.Close()
        'con.Close()
        '第二个查询
        sqlstr = "select 所在科室,姓名 from jbxx"
        datatab = conn(sqlstr)
        TreeView1.Nodes.Add(nod(i).Text)
        While datatab.Read() ''这里的值为什么为假？
            datatab.GetString(0)
            While i = 0 'I已经为6了。
                If nod(i).Text = datatab.GetString(0) Then
                    nod(i).Nodes.Add(datatab.GetString(1)) '创建第一个查询出来的子节点。
                End If
                i = i - 1
            End While
        End While
        con.Close()
    End Sub
    Private Function conn(ByVal sqlstr As String)
        con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data source=D:\temp\aa\data.mdb"
        Dim oada As New OleDb.OleDbDataAdapter(sqlstr, con)
        con.Open()
        Dim ds As New DataSet
        oada.Fill(ds)
        Return ds.Tables(0).CreateDataReader
    End Function
End Class

 While i = 0 'I已经为6了。
  If nod(i).Text = datatab.GetString(0) Then
  nod(i).Nodes.Add(datatab.GetString(1)) '创建第一个查询出来的子节点。
  End If
  i = i - 1
  End While

------解决方案--------------------
http://user.qzone.qq.com/631582825/blog/1320153235
这个是我解决问题后的正确源代码。

------解决方案--------------------
http://blog.csdn.net/w200221626/article/details/6699619
看看这个也许会有帮助