private void button2_Click(object sender, EventArgs e)
        {
            List <BllUser> newRecievers = new List <BllUser>();
            int            nodeCount    = 0;

            foreach (TreeNode groupNode in treeView1.Nodes)
            {
                foreach (TreeNode userNode in groupNode.Nodes)
                {
                    if (userNode.Checked)
                    {
                        newRecievers.Add(Users[userNode.Index + nodeCount]);
                    }
                }
                nodeCount += groupNode.GetNodeCount(false);
            }

            try
            {
                IEventCRUD eventCRUD = new EventCRUD(serverInstance.server);
                eventCRUD.UpdateRecieversAndSendOnEvent(Event, newRecievers);
                Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }