How to bind object to property on click using CoC DotVVM

Question

I created my own Code only Component for Accordion. It looks like on picture below.

Lines with blue arrows are article sections and those with red line are articles. What I want to archieve is on page load I will get only root article sections, nothing else. When I will click on "TEST" I will send get request with ID to load more items.

My problem is I cannot get object on which I clicked into my property in ViewModel. I created SelectedValueProperty for this purpose and register it in static constructor. After that I override GetControlBinding method and added property into group. However when I click on item in my view, nothing is assigned to my SelectedValueProperty.

Here is my code of CoC

public class Accordion : HierarchyItemsControlBase
{
    public static readonly DotvvmProperty SelectedValuesProperty;
    public static readonly DotvvmProperty ChangedProperty;
    protected override HtmlContents CreateItemContents(DataItemContainer dataItem)
    {
        var contents = base.HtmlFactory.CreateContents();
        return contents;
    }

    public Accordion() : base("div")
    {

    }

    static Accordion()
    {
        SelectedValuesProperty = DotvvmProperty.Register<IEnumerable, Accordion>(c => c.SelectedValues, null, false);
        ChangedProperty = DotvvmProperty.Register<Command, Accordion>(c => c.Changed, null);
    }

    #region Properties

    public List<ArticleSectionListDTO> DataSource
    {
        get => (List<ArticleSectionListDTO>)GetValue(DataSourceProperty);
        set => SetValue(DataSourceProperty, value);
    }

    public IEnumerable SelectedValues
    {
        get => GetValue(SelectedValuesProperty, true) as IEnumerable;
        set => SetValue(SelectedValuesProperty, value);
    }

    public Command Changed
    {
        get => GetValue(ChangedProperty) as Command;
        set => SetValue(ChangedProperty, value);
    }

    public Command Click { get; set; }
    #endregion


    protected override ControlBindingGroup GetControlBinding()
    {
        var controlBinding = base.GetControlBinding();
        controlBinding.Add(this, SelectedValuesProperty);
        return controlBinding;
    }


    protected override void AddAttributesToRender(IHtmlWriter writer, IDotvvmRequestContext context)
    {
        writer.AddControlKnockoutDataBind<Accordion>(GetControlBinding());

        Attributes.Add("class", "accordion");
        base.AddAttributesToRender(writer, context);

        var clickBinding = GetCommandBinding(ChangedProperty);
        if (clickBinding != null)
        {
            writer.AddAttribute("onclick", KnockoutHelper.GenerateClientPostBackScript(nameof(Click), clickBinding, this), true, ";");
        }
    }

    public void DataBind(IDotvvmRequestContext context)
    {
        //some code here
    }

    public void DataBindItem(DotvvmControl parent, ArticleSectionListDTO item, IDotvvmRequestContext context)
    {
         //some code here
    }

    protected override void RenderContents(IHtmlWriter writer, IDotvvmRequestContext context)
    {
        DataBind(context);
        base.RenderContents(writer, context);
    }
}

Here is my ViewModel where AccordionList serves as datasource and AccordionSelected has to serve as a storage of object on which I clicked.

public List<ArticleSectionListDTO> AccordionList { get; set; } = new List<ArticleSectionListDTO>();
public List<ArticleSectionListDTO> AccordionSelected { get; set; } = new List<ArticleSectionListDTO>();

How I use it in view

<coc:Accordion DataSource="{value: AccordionList}" 
       ItemChildrenBinding="{{value: HasCategories}}" 
       SelectedValues="{{value: AccordionSelected}}">
</coc:Accordion>