The story
Apparently from an actual attempt to organise a Bush Festival in Sydney in 1919; the idea then being extended to the present figurative use.
Etymology from Wiktionary, CC BY-SA 4.0.
bush week
Today it means: An imagined or symbolic time when assumedly unsophisticated people from the countryside come to the city, likely to be preyed on by tricksters there, or who are unaware of social norms in the city. Full definition →