Garden climbing frame (7)
(Other definitions for pergola that I've seen before include "Overhanging garden structure" , "Arched frame for climbing plants" , "lattice" , "Trellis for climbing plants" , "Framework for climbers" .)
'garden climbing frame' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for trellis that I've seen before include "Latticework support for plants" , "Structure supporting climbing plants" , "Garden climbing frame" , "Garden climber support" , "Arch of latticework" .)