A long expression that specifies the index of the group node being removed.
Use the RemoveGroup method to remove a group node. Use the AddGroup method to
add new nodes in the same group ( multiple parents ). Use the IsGroup
property to specify whether a node was added using the AddGroup method. Use the
CountGroup and
Group properties to access or enumerate the group nodes collection. Use the InflateGroupY
property to specify the indentation of the group on vertical axis.