Actalluy, "Gist" code doesnt use "R-tree". There are "AM extention" functions and "gistproc.c" file which split to "R-tree". However, I checked on that the 'gistproc.c' function didnt be called when i was generating a 'index' with using 'gist' even though it was spatial data. So, I want to know how to use 'R-tree' with "gist".