CREATE TABLE AnaKategori
(
	id int identity(1,1),
	AnaKategori varchar(50),
	Aktif int default 1
	primary key (id)
)

CREATE TABLE Kategori
(
	id int identity(1,1),
	AnaKategoriId int,
	Kategori varchar(50),
	Aktif int default 1
	primary key (id)
)

<asp:TreeView ID="TreeView1" runat="server" ImageSet="XPFileExplorer" NodeIndent="15">
    <HoverNodeStyle Font-Underline="True" ForeColor="#6666AA" />
    <NodeStyle Font-Names="Tahoma" Font-Size="8pt" ForeColor="Black" HorizontalPadding="2px"
        NodeSpacing="0px" VerticalPadding="2px"></NodeStyle>
    <ParentNodeStyle Font-Bold="False" />
    <SelectedNodeStyle BackColor="#B5B5B5" Font-Underline="False" HorizontalPadding="0px"
        VerticalPadding="0px" />
</asp:TreeView>

using System.Data;
using System.Data.SqlClient;
using System.Configuration;

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = this.GetData("SELECT id, AnaKategori FROM AnaKategori WHERE Aktif = 1");
        this.PopulateTreeView(dt, 0, null);
    }
}
 
private void PopulateTreeView(DataTable dtParent, int parentId, TreeNode treeNode)
{
    foreach (DataRow row in dtParent.Rows)
    {
        TreeNode child = new TreeNode
        {
            Text = row["Name"].ToString(),
            Value = row["Id"].ToString()
        };
        if (parentId == 0)
        {
            TreeView1.Nodes.Add(child);
            DataTable dtChild = this.GetData("SELECT id,Kategori FROM Kategori WHERE Aktif = 1 and AnaKategoriId = " + child.Value);
            PopulateTreeView(dtChild, int.Parse(child.Value), child);
        }
        else
        {
            treeNode.ChildNodes.Add(child);
        }
    }
}
 
private DataTable GetData(string query)
{
    DataTable dt = new DataTable();
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.CommandType = CommandType.Text;
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                sda.Fill(dt);
            }
        }
        return dt;
    }
}