I want the data coming from the database to be sorted as subheadings, first the Thickness will be given and the Genres belonging to that thickness will be displayed. When I click, it will open under it, and then I want the colors of the type we pressed to appear.

My code is as below.

using System;
using System.Data;
using System.Data.SqlClient;
using System.Threading;
using System.Windows.Forms;
using DevExpress.XtraGrid.Views.Grid;

namespace Randuman
{
    public partial class Iplık_Cozgu : Form
    {
        public Iplık_Cozgu()
        {
            InitializeComponent();
        }

        sqlbaglanti bgl = new sqlbaglanti();

        private DataTable iplikTable;

        private void InitializeTables()
        {
            iplikTable = new DataTable();
            iplikTable.Columns.Add("Kalınlık", typeof(float));
            iplikTable.Columns.Add("Cins", typeof(string));
            iplikTable.Columns.Add("Renk", typeof(string));
            iplikTable.Columns.Add("Birim", typeof(string));
            iplikTable.Columns.Add("TARIH", typeof(string));
        }

        private void SetupGridControl()
        {
            gridControl1.DataSource = iplikTable;

            GridView kalinlikView = gridControl1.MainView as GridView;
            GridView cinsView = new GridView(gridControl1);
            GridView renkView = new GridView(gridControl1);

            gridControl1.LevelTree.Nodes.Add("Kalınlık", cinsView);
            gridControl1.LevelTree.Nodes.Add("Cins", renkView);

            cinsView.PopulateColumns(iplikTable);
            renkView.PopulateColumns(iplikTable);

            // Set Relations
            gridControl1.LevelTree.Nodes["Kalınlık"].RelationName = "Kalınlık_Cins";
            gridControl1.LevelTree.Nodes["Cins"].RelationName = "Cins_Renk";
        }

        private void LoadData()
        {
            // Load Iplik Data
            SqlCommand cmd = new SqlCommand($"SELECT Kalınlık, Cins, Renk, Birim, TARIH FROM {config.IPLIK} ORDER BY Kalınlık, Cins, Renk", bgl.Connection());
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.Fill(iplikTable);
            bgl.Connection().Close();
        }

        private void Clear()
        {
            CozguName.Text = string.Empty;
            Tel.Text = string.Empty;
            En.Text = string.Empty;
        }

        private void ClearIplıkAll()
        {
            kalın.Text = string.Empty;
            birim.Text = string.Empty;
            cins.Text = string.Empty;
            renk.Text = string.Empty;
        }

        private void ClearSave()
        {
            renk.Text = string.Empty;
        }

        private void ListDbCombo()
        {
            SqlCommand cmd = new SqlCommand($"SELECT DISTINCT Renk from {config.IPLIK}", bgl.Connection());
            SqlDataReader dr = cmd.ExecuteReader();
            while (dr.Read())
            {
                renk.Properties.Items.Add(dr[0].ToString());
            }
            bgl.Connection().Close();
        }

        private void simpleButton1_Click(object sender, EventArgs e)
        {
            try
            {
                SqlCommand cmd = new SqlCommand($"insert into {config.COZGU} (Ad,Tel,En,TARIH) values(@p1,@p2,@p3,@p4)", bgl.Connection());
                cmd.Parameters.AddWithValue("@p1", CozguName.Text.Trim());
                cmd.Parameters.AddWithValue("@p2", Tel.Text);
                cmd.Parameters.AddWithValue("@p3", En.Text);
                cmd.Parameters.AddWithValue("@p4", DateTime.Now.ToString("dd.MM.yyyy - HH:mm"));
                cmd.ExecuteNonQuery();
                bgl.Connection().Close();
                MessageBox.Show("Çözgü Başarıyla Veritabanına Kaydedildi.", "Kayıt Başarılı!", MessageBoxButtons.OK, MessageBoxIcon.Information);
                Thread.Sleep(1);
                Clear();
            }
            catch (SqlException ex)
            {
                MessageBox.Show("VeriTabanı Hatası: " + ex.Message, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            catch (Exception ex)
            {
                MessageBox.Show("Program Hatası: " + ex.Message, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }

        private void simpleButton2_Click(object sender, EventArgs e)
        {
            Clear();
        }

        private void simpleButton4_Click(object sender, EventArgs e)
        {
            try
            {
                SqlCommand cmd = new SqlCommand($"insert into {config.IPLIK} (Kalınlık,Birim,Cins,Renk,TARIH) values(@p1,@p2,@p3,@p4,@p5)", bgl.Connection());
                cmd.Parameters.AddWithValue("@p1", kalın.Text.Trim());
                cmd.Parameters.AddWithValue("@p2", birim.Text);
                cmd.Parameters.AddWithValue("@p3", cins.Text);
                cmd.Parameters.AddWithValue("@p4", renk.Text);
                cmd.Parameters.AddWithValue("@p5", DateTime.Now.ToString("dd.MM.yyyy - HH:mm"));
                cmd.ExecuteNonQuery();
                bgl.Connection().Close();
                MessageBox.Show("İplik " + cins.Text + " Başarıyla Veritabanına Kaydedildi.", "Kayıt Başarılı!", MessageBoxButtons.OK, MessageBoxIcon.Information);
                Thread.Sleep(1);
                ClearSave();
            }
            catch (FormatException ex)
            {
                MessageBox.Show("Kullanıcı Hatası: " + ex.Message, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            catch (SqlException ex)
            {
                MessageBox.Show("VeriTabanı Hatası: " + ex.Message, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            catch (Exception ex)
            {
                MessageBox.Show("Program Hatası: " + ex.Message, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }

        private void Iplık_Cozgu_Load(object sender, EventArgs e)
        {
            InitializeTables();
            LoadData();
            SetupGridControl();
        }

        private void XtraTabControl1_SelectedPageChanged(object sender, DevExpress.XtraTab.TabPageChangedEventArgs e)
        {
            if (e.Page.Text == "Çözgü Kayıt")
            {
            }
            else if (e.Page.Text == "İPLİK KAYIT")
            {
                LoadData();
                ListDbCombo();
            }
        }

        private void simpleButton3_Click(object sender, EventArgs e)
        {
            ClearIplıkAll();
        }
    }
}