Sitecore - how to show templates under specific folder, inside insert options context menu

Lets say the user itself is able to add new branch templates.

And on a homepage item, insert options must consist of items inside that branch templates folder.

In sitecore, insert options can only be set to specific items. When I select a folder as an insert option, sitecore shows that folder item (which is perfectly normal).

I need to make something like either showing items dynamically inside a specific folder, or setting the starting path of insert options browsing dialog.

Is any of this possible ?

Blog post: https://sitecorealekseyshevchenko.wordpress.com/2017/09/19/dynamic-insert-options/

Create 'Dynamic Insert Option' template wich contains the only field 'Starting Path' type of 'Droptree' and source value is '{3C1715FE-6A13-4FCF-845F-DE308BA9741D}' - id of '/sitecore/templates' item.

Then add 'Dynamic Insert Option' template to list of templates in 'Base template' field of the template which should have dynamic insert options.

Patch 'uiGetMasters' processor with such config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <processors>
      <uiGetMasters>
        <processor mode="on"
                   type="DynamicInsertOption.Processors.GetDynamicInsertOption, DynamicInsertOption"
                   patch:before="processor[@type='Sitecore.Pipelines.GetMasters.CheckSecurity, Sitecore.Kernel']" />
      </uiGetMasters>
    </processors>
  </sitecore>
</configuration>

Implement GetDynamicInsertOption processor:

namespace DynamicInsertOption.Processors
{
    using Sitecore.Data.Items;
    using Sitecore.Diagnostics;
    using Sitecore.Pipelines.GetMasters;

    public class GetDynamicInsertOption
    {
        public void Process(GetMastersArgs args)
        {
            Assert.ArgumentNotNull(args, "args");

            var startingPath = args.Item["Starting Path"];

            if (!string.IsNullOrEmpty(startingPath))
            {
                for (int i = args.Masters.Count - 1; i > -1; i--) { args.Masters.RemoveAt(i); }

                var startingFolder = args.Item.Database.GetItem(startingPath);

                foreach (Item master in startingFolder.Children) { args.Masters.Add(master); }
            }
        }
    }
}

The result see on pic below: