ASP.NET

public partial class MasterPage : System.Web.UI.MasterPage
{
    SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["SilverOnline"].ConnectionString);
    protected void Page_Load(object sender, EventArgs e)
    {
        populatemenu();
    }
    private void populatemenu()
    {
        //SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["Jajaipur"].ConnectionString);
        //Menu mnu = new Menu();
       
        SqlDataReader dr = null;
        string str = "Select * From Cat1";
        SqlCommand cmd = new SqlCommand(str, conn);
        conn.Open();
        dr = cmd.ExecuteReader();
        while (dr.Read())
        {
            MenuItem mt = new MenuItem();
            mt.Text = dr["CatName"].ToString();
            mt.Value = dr["Cat1ID"].ToString();
            mt.NavigateUrl = "Displaymenu.aspx?id=" + mt.Value;
            string s = mt.Value;
            conn.Close();
            string str1 = "Select * From Cat2 where(Cat1ID='" + s + "')";
            SqlCommand cmd1 = new SqlCommand(str1, conn);
            conn.Open();
            dr = cmd1.ExecuteReader();
            while (dr.Read())
            {
                MenuItem mf = new MenuItem();
                mf.Text = dr["Cat2Name"].ToString();
                mf.Value = dr["Cat2ID"].ToString();
                mf.NavigateUrl = "Displaysubmenu.aspx?id=" + mf.Value;
                mt.ChildItems.Add(mf);
                
            }
            
        }
        conn.Close();
        Menu1.Items.Add(mt);
        
        
    }
}

<asp:WizardStep ID="BusinessUnitWizardsStep" runat="server" StepType="Step" Title="BusinessUnits">
                   <br />
                   <table class="FormTable">
                       <tr>
<div id ="BusinessUnitsPanel1" runat="server" style="width:100%;height:330px;overflow:auto;">
                                  <asp:Label ID="emptyTextLabel" runat="server" CssClass="ErrorMessagesLabel" Text="No Records found" />
                                   <asp:UpdatePanel ID="TreeViewUpdate" runat="server" ChildrenAsTriggers="true">
                                       <ContentTemplate>
                                           <asp:TreeView onclick="postbackOnCheck(event,'ctl00_PCMSMainContent_CreateDocumentWizard_TreeViewUpdate')" ID="AvailableBusinessUnitsTreeView"
                                               runat="server" Height="100%" Width="50%" ShowLines="true" ShowCheckBoxes="All" ExpandDepth="1"
                                               OnTreeNodePopulate="AvailableBusinessUnitsTreeView_TreeNodePopulate"
                                               OnTreeNodeCheckChanged="AvailableBusinessUnitsTreeView_TreeNodeCheckChanged" EnableClientScript="false">
                                               <ParentNodeStyle Font-Bold="False" />
                                               <HoverNodeStyle Font-Underline="True" ForeColor="#6666AA" />
                                               <SelectedNodeStyle BackColor="#B5B5B5" Font-Underline="False" HorizontalPadding="0px"
                                               VerticalPadding="0px" />
                                               <NodeStyle Font-Names="Tahoma" Font-Size="10pt" ForeColor="Black" HorizontalPadding="2px"
                                               NodeSpacing="0px" VerticalPadding="2px" />
                                           </asp:TreeView>
                                       </ContentTemplate>
                                   </asp:UpdatePanel>
                              </div>

protected void CreateDocumentWizard_ActiveStepChanged(object sender, EventArgs e)
{
   if (CreateDocumentWizard.ActiveStep == BusinessUnitWizardsStep)
   {
      EnableDisableNextButton(false);
   }
}

 private void EnableDisableNextButton(bool isEnable)
    {
        Button btnnext = (Button)CreateDocumentWizard.FindControl("StepNavigationTemplateContainerID").FindControl("StepNextButton");
        if (btnnext != null)
        {
            btnnext.Enabled = isEnable ? true : false;
        }
          
    }

 protected void AvailableBusinessUnitsTreeView_TreeNodeCheckChanged(object sender, TreeNodeEventArgs e)
{
   if (e.node.Checked)
   {
      //Code for what to do if checked.
    } 
    EnableDisableNextButton(true);