Accessor of the level-indentation of the gtk-tree-view class.
The gtk-tree-view-level-indentation slot access function returns the amount, in pixels, of extra indentation for child levels in the tree view.
The (setf gtk-tree-view-level-indentation) slot access function sets the amount of extra indentation for child levels to use in the tree view in addition to the default indentation. The value should be specified in pixels, a value of 0 disables this feature and in this case only the default indentation will be used. This does not have any visible effects for lists.