public void saveToFile() {
            XmlWriter xmlWriter = XmlWriter.Create(FileName);
            xmlWriter.WriteStartDocument();
            xmlWriter.WriteStartElement("students");
            foreach (Student s in entities) {
                xmlWriter.WriteStartElement("student");

                xmlWriter.WriteStartElement("id");
                xmlWriter.WriteString(s.Id.ToString() + "");
                xmlWriter.WriteEndElement();

                xmlWriter.WriteStartElement("nume");
                xmlWriter.WriteString(s.Nume);
                xmlWriter.WriteEndElement();

                xmlWriter.WriteStartElement("grupa");
                xmlWriter.WriteString(s.Grupa.ToString() + "");
                xmlWriter.WriteEndElement();

                xmlWriter.WriteStartElement("email");
                xmlWriter.WriteString(s.Email);
                xmlWriter.WriteEndElement();

                xmlWriter.WriteStartElement("profesor");
                xmlWriter.WriteString(s.Profesor);
                xmlWriter.WriteEndElement();

                xmlWriter.WriteEndElement();
            }
            xmlWriter.WriteEndElement();
            xmlWriter.WriteEndDocument();
            xmlWriter.Close();

        }