Gets the height of a #GTree.
If the #GTree contains no nodes, the height is 0. If the #GTree contains only one root node the height is 1. If the root node has children the height is 2, etc.
the height of @tree
See Implementation
Gets the height of a #GTree.
If the #GTree contains no nodes, the height is 0. If the #GTree contains only one root node the height is 1. If the root node has children the height is 2, etc.