private void DepartmentsTree_SelectionChanged(object sender, EventArgs _)
        {
            TreeNode node = DepartmentsTree.SelectedNode;

            Employee[] emps = ((node != null ? (Employee[])Tree.GetTreeNodeData(node) : null) ?? new Employee[0]);
            EmployeesGrid.BeginRebuild();
            foreach (Employee e in emps)
            {
                EmployeesGrid.AddItem(GetGridTexts(e), e);
            }
            EmployeesGrid.AddItem(GetGridTexts(null), null);
            EmployeesGrid.EndRebuild();
        }