The JSON is invalid. A collection is not to be represented by {}. It stands for an object. A collection/array is to be represented by [] with commaseparated objects.

Here's how the JSON should look like:

{
    users:[{
        name: "name1",
        email: "email1",
        friends:[{
            name: "name2",
            email: "email2",
            friends:[{
                name: "name3",
                email: "email3"
            },
            {
                name: "name4",
                email: "email4"
            }]
        }]
    }]
}

(note that I added one more friend to the deepest nested friend, so that you understand how to specify multiple objects in a collection)

Given this JSON, your wrapper class should look like this:

public class Data {
    private List<User> users;
    // +getters/setters
}

public class User {
    private String name;
    private String email;
    private List<User> friends;
    // +getters/setters
}

and then to convert it, use

Data data = gson.fromJson(this.json, Data.class);

and to get the users, use

List<User> users = data.getUsers();