EF Core Include Discover How to Retrieve Related Objects in LINQ

public class Customer
{
    public int CustomerId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Address { get; set; }
    public virtual List<Invoice> Invoices { get; set; }
}

public class Invoice
{
    public int InvoiceId { get; set; }
    public DateTime Date { get; set; }
    public int CustomerId { get; set; }
    [ForeignKey("CustomerId")]
    public Customer Customer { get; set; }
    public List<InvoiceItem> Items { get; set; }
}

public class InvoiceItem
{
    public int InvoiceItemId { get; set; }
    public int InvoiceId { get; set; }
    public string Code { get; set; }
    [ForeignKey("InvoiceId")]
    public virtual Invoice Invoice { get; set; }
}

using (var context = new MyContext())
{
    var customers = context.Customers
        .Include(c => c.Invoices)
        .ToList();
}

using (var context = new MyContext())
{
    var customers = context.Customers
        .Include(i => i.Invoices)
            .ThenInclude(it => it.Items)
        .ToList();
}