Level and KeyPosition in Tree Views
A tree view which is a hierarchical list has two properties other lists do not have: Level and KeyPosition. Level specifies which level in the hierarchy the column belongs to and KeyPosition specifies whether the column is used as a key for this level of the list. Every level in a tree view except the last must have a field with a KeyPosition specified.
For example a value of 1 for Level specifies that the column is shown on the first level of the tree view. A value of 0 for KeyPosition specifies that the column is not used as the key for this level. There can be more than one key column for a level in which case the KeyPosition determines their order. Note however that only one column can be visible per level.