Can't draw more than one trendline in custom indicator

Hi, for learning purpose I am coding a custom indicator. It should draw a trendline on 5 bars every 20 bars. But when it draws new trendline the previous one disapear. Can you help me please?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using cAlgo.API;
using cAlgo.API.Collections;
using cAlgo.API.Indicators;
using cAlgo.API.Internals;

namespace cAlgo
{
    [Indicator(AccessRights = AccessRights.None)]
    public class testdrawline : Indicator
    {
        [Parameter(DefaultValue = "Hello world!")]
        public string Message { get; set; }

        [Output("Main")]
        public IndicatorDataSeries Result { get; set; }
        
        int period = 20;
        
        
        protected override void Initialize()
        {
            // To learn more about cTrader Automate visit our Help Center:
            // https://help.ctrader.com/ctrader-automate
            
            Print(Message);
        }

        public override void Calculate(int index)
        {
            // Calculate value at specified index
            // Result[index] = 
            if (index % period != 0)return;
            
            Chart.DrawTrendLine("line", Bars[index].OpenTime, Bars[index].Close, Bars[index - 5].OpenTime, Bars[index - 5].Close, "Yellow").IsInteractive = true;
            
        }
    }
}