Using horizontal scrolling is very easy, even if multiple columns are used.  The Scrollbars property is used to define the desired scroll bars.

Once all items have been added to the tree control, the Items.RecalcHorizontalExtent method must be used to allow the control to determine the optimal horizontal scrolling extent, which is determined by column widths and the text in the last column.

The OffsetChange event occurs when the tree control is scrolled horizontally by the user.

Even if horizontal scroll bars are defined, Items.RecalcHorizontalExtent must be used after all items have been added, otherwise the horizontal scroll bar will not be enabled or updated.