Add Dummy cube
Dummy cube is invisible object intended for grouping of other objects.
Note: any other object can be used as container to group other objects. Like this object Frustum is container for object Cone in the example of tree of objects and object Easy 3D Objects is container for all objects which are included in a tree.
Parameters Name, Path..., Show axes, Angle, Scale are general for all objects. They are considered here.
Group Sizes sets the sizes of object (field Size) and defines visibility of dummy cube edges (flag Show edges). You can see dummy cube edges as dashed line.