Формирование списка студентов - найти ошибку в коде - C#

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
 
        {
            XDocument xml = XElement.Load(Students.xml);
            string Surname = textBox1.Text;
            string Name = textBox2.Text;
            string Otchestvo = textBox3.Text;
            string fio = string.Format("{0} {1}.{2}.", Surname.Substring(0, 1).ToUpper() + Surname.Substring(1),
                                                                               Name.Substring(0, 1).ToUpper(),
                                                                               Otchestvo.Substring(0, 1).ToUpper());

        }
 
        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            ListBox lb = sender as ListBox;
            if (lb.SelectedItem != null)
            {
                Student tvr = lb.SelectedItem as Student;
                textBox1.Text = tvr.Surname;
                textBox2.Text = tvr.Name;
                textBox3.Text = tvr.Otchestvo;

            }
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
            string adr;
            Students student = new Students();
            adr ="Students.xml";
                XDocument read = new XDocument();
                read = XDocument.Load(adr);
                XElement root = read.Root;
                foreach (XElement element in root.Elements())
                {
                    Student tvr = new Student(element);
                    student.Add(tvr);
                }
         //  }
            listBox1.DataSource = student;
            listBox1.DisplayMember = "Fio";
        }
 
        private void button2_Click(object sender, EventArgs e)
        {
            listBox1.Items.Clear();
        }

        }
 
    }

namespace WindowsFormsApplication1
{
    class Student
    {
        public string Surname { get; set; }
        public string Name { get; set; }
        public string Otchestvo { get; set; }
        public string Fio
        {
            get
            {
                try
                {
                    return string.Format("{0} {1}.{2}.", Surname.Substring(0, 1).ToUpper() + Surname.Substring(1),
                                                                               Name.Substring(0, 1).ToUpper(),
                                                                               Otchestvo.Substring(0, 1).ToUpper());
                }
                  
                catch {return "Ошибка!!!";}
            }
 
            }
        }
             public Student(XElement element)
        {
            
            Surname = element.Element("Surname").Value;
            Name = element.Element("Name").Value;
            Otchestvo = element.Element("Otchestvo").Value;
            
        }

    }
    class Students : List<Student>
    {
    }