Finds a Node in a tree.
the root Node of the tree to search
the order in which nodes are visited - g_in_order, g_pre_order, g_post_order, or g_level_order
which types of children are to be searched, one of g_traverse_all, g_traverse_leaves and g_traverse_non_leaves
the data to find
the found Node, or null if the data is not found