property Column.LevelKey as Variant
Retrieves or sets a value that indicates the key of the column's level.

Variant A Variant expression that indicates the key of the column's level.
By default, the LevelKey is empty. The control's header displays multiple levels if there are two or more neighbor columns with the same non empty level key. The HeaderHeight property specifies the height of one level when multiple levels header is on. Use the BackColorLevelHeader property to specify the control's level header area. Use the PictureLevelHeader property to assign a picture on the control's header. The BackColorHeader property specifies the background color for column's captions. Use the LevelCount property to specify the number of levels being displayed in the chart's header.