Edit in JSFiddle

var flexGrid = new wijmo.grid.FlexGrid('#flexGrid', {
  itemsSource: [
    {id: 1, name: 'US'},
    {id: 2, name: 'US'},
    {id: 3, name: 'US'},
    {id: 4, name: 'Germany'},
    {id: 5, name: 'Germany'},
  ],
  columns: [
    {binding: 'id'},
    {binding: 'name', allowMerging: true},
  ],
  allowMerging: 'Cells',
  selectionMode: 'ListBox',
});

<div id="flexGrid"></div>