Problem in disposing object

private void button_Click(object sender, EventArgs e)
        {
            using (DataTable dt = new DataTable())
            {
                dt.Columns.Add("Name", typeof(string));
                using (CheckingPerformance objCheckingPerformance = new CheckingPerformance())
                {
                 objCheckingPerformance.method(objCheckingPerformance.method_row(dt));

                }
            }
        }

public class CheckingPerformance:IDisposable
    {
        public DataTable dt = null;
        public DataRow dr = null;
        private bool _disposed;

        public DataTable method(DataTable pdt)
        {
            return pdt;
            
        }

        public DataTable method_row(DataTable dt)
        {
            
                for (int i = 0; i <= 200000; i++)
                {

                    dt.Rows.Add("admin" + i.ToString());
                }
                return dt;
            
        }

            

        protected virtual void Dispose(bool disposing)
        {
            if (!_disposed)
            {
                if (disposing)
                {
                    // Dispose managed resources
                    //if (_stream != null) _stream.Dispose();
                    if (dt != null) dt = null;
                    if (dr != null) dr = null;
                }
 
                // Dispose unmanaged resources
                //_handle = IntPtr.Zero;
 
                //_stream = null;
                _disposed = true;
            }
        }
 
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        ~CheckingPerformance()
        {
            Dispose(false);
        }

    }