public class GroupElement : Element, ILayoutElementContainer, ArcGIS.Desktop.Mapping.IElementParent, System.ComponentModel.INotifyPropertyChanged, System.IComparable, System.IEquatable<Element>  

//Create an empty group element at the root level of the contents pane

//Create on worker thread
await QueuedTask.Run(() =>
{
  GroupElement grp1 = LayoutElementFactory.Instance.CreateGroupElement(layout);
  grp1.SetName("Group");
});

// *** or ***

//Create a group element inside another group element

//Find an existing group element
GroupElement existingGroup = layout.FindElement("Group") as GroupElement;
      
//Create on worker thread
await QueuedTask.Run(() =>
{
  GroupElement grp2 = LayoutElementFactory.Instance.CreateGroupElement(existingGroup);
  grp2.SetName("Group in Group");
});

//Create a group with a list of elements at the root level of the contents pane.

//Find an existing elements
Element scaleBar = layout.FindElement("Scale Bar") as Element;
Element northArrow = layout.FindElement("North Arrow") as Element;
Element legend = layout.FindElement("Legend") as Element;

//Construct a list and add the elements
List<Element> elmList = new List<Element>
{
  scaleBar,
  northArrow,
  legend
};

//Perform on the worker thread
await QueuedTask.Run(() =>
{
  GroupElement groupWithListOfElementsAtRoot = LayoutElementFactory.Instance.CreateGroupElement(layout, elmList);
  groupWithListOfElementsAtRoot.SetName("Group with list of elements at root");
});


// *** or ***


//Create a group using a list of element names at the root level of the contents pane.

//List of element names
var elmNameList = new[] { "Table Frame", "Chart Frame" };

//Perform on the worker thread
await QueuedTask.Run(() =>
{
  GroupElement groupWithListOfElementNamesAtRoot = LayoutElementFactory.Instance.CreateGroupElement(layout, elmNameList);
  groupWithListOfElementNamesAtRoot.SetName("Group with list of element names at root");
});