thing.cs

public class Project
{
    public int ID { get; set; }
    public string DisplayName { get; set; }
    public Organisation OrganisationOwner { get; set; }
}

public class Organisation
{
    public int ID { get; set; }
    public string DisplayName { get; set; }
    public List<ApplicationUser> Members { get; set; }
    public List<Project> Projects { get; set; }
}