public class foo
{
    public int id {get; set;}

    public string name{ get; set; }

    public ICollection<bar> bar{ get; set; }
}

public class bar
{
    public int id {get; set;}

    public string name{ get; set; }
}

foo fooexample = new foo();
foreach (var object in exceldata)
{
    fooexample.id = exceldata.id;
    fooexample.bar.id = exceldata.bar.id;
    // <-- how do I do this? if I need to initialize it, how?
}