public class HomeSection2
{
    public HomeSection2()
    {
        HomeSection2Detail = new List<HomeSection2Detail>();
    }

    public Guid ID { get; set; }
    public string Title { get; set; }
    public string Header { get; set; }

    public virtual List<HomeSection2Detail> HomeSection2Detail { get; set; }
}

public class HomeSection2Detail
{
    public Guid ID { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
    public string Link { get; set; }
    public int? Sequence { get; set; }

    public virtual HomeSection2 HomeSection2 { get; set; }
}

var obj2detail = obj2.HomeSection2Detail.Where(w => w.ID == detail.ID).FirstOrDefault();
                            if (obj2detail != null) { obj2.HomeSection2Detail.Remove(obj2detail); }