Add multiple items to a list

In modern C# using extension methods, generics, and the params keyword, you can create a generic method on the List class that allows you to add an indefinite number of items to a list containing any type:

static class ListExtensions 
{
  static public void Add<T>(this List<T> list, params T[] additions)
  {
    foreach(T addition in additions)
    {
      list.Add(addition)
    }
  }
}

Example usage using a list of strings and a list of integers:

var stringList = new List<string>();
stringList.Add("Hello", "World", "!");

var intList = new List<int>();
intList.Add(1, 2, 3, 4, 5);

Thanks to AddRange:

Example:

public class Person
{ 
    private string Name;
    private string FirstName;

    public Person(string name, string firstname) => (Name, FirstName) = (name, firstname);
}

To add multiple Person to a List<>:

List<Person> listofPersons = new List<Person>();
listofPersons.AddRange(new List<Person>
{
    new Person("John1", "Doe" ),
    new Person("John2", "Doe" ),
    new Person("John3", "Doe" ),
 });

Code check:

This is offtopic here but the people over at CodeReview are more than happy to help you.

I strongly suggest you to do so, there are several things that need attention in your code. Likewise I suggest that you do start reading tutorials since there is really no good reason not to do so.

Lists:

As you said yourself: you need a list of items. The way it is now you only store a reference to one item. Lucky there is exactly that to hold a group of related objects: a List.

Lists are very straightforward to use but take a look at the related documentation anyway.

A very simple example to keep multiple bikes in a list:

List<Motorbike> bikes = new List<Motorbike>();

bikes.add(new Bike { make = "Honda", color = "brown" });
bikes.add(new Bike { make = "Vroom", color = "red" });

And to iterate over the list you can use the foreach statement:

foreach(var bike in bikes) {
     Console.WriteLine(bike.make);
}

Another useful way is with Concat.
More information in the official documentation.

List<string> first = new List<string> { "One", "Two", "Three" };
List<string> second = new List<string>() { "Four", "Five" };
first.Concat(second);

The output will be.

One
Two
Three
Four
Five

And there is another similar answer.