Setting Value to the List property of a class object variable in c#

i have a class,

public class Test
{
    public int b { get; set; }
    public int c { get; set; }
    public List<Doc> doc=new List<Doc>();
}

Public Class Doc
{
    public int a { get; set; }
    public int b { get; set; }
} 

Here, i can set the value to the Test Variables like,

Test test = new Test();
string var1= "b";
PropertyInfo pi= test.GetType().GetProperty(var1);
pi.SetValue(test, Convert.ChangeType(1,pi.PropertyType), null);

so i can get test.b as 1. Likewise i need to set the value for doc. How do i achieve this. Thanks for your time.