( From this thread : )Step :
1)
Open Extractor ->Open Data.pk2 go to res\bldg\common\event-xmas\x_mas_tree_b.bsr and extract.
2)Rename it to a building you want to replace . Example w_cd_portal.bsr .
3) Open Editor ,File -> Open the data.pk2
''Step 1: Chose the imput file or folder" -> Select file -> Select the w_cd_portal.bsr
Note : w_cd_portal.bsr is the tree modified
''Step 2 : Enter the path the selected file etc... "
Write \res\bldg\china\dunhuang\buildings\
If it doesn't work remove the ''\'' then hit Import and that's the deal
Good luck
Some credits go to perrytje and Vanillous
