Illustrated by Terry Denton, The 65 Storey Treehouse is the fastest selling Australian book in the last 10 years.
The book�s release on August 12 was met by eager fans queuing outside book stores to get a copy.
First-day sales reached more than 2250.
Dymocks national buying manager Sophie Higgins said the next best-selling author was Matthew Reilly with his previous title Five Greatest Warriors in 2009.
Griffiths� previous instalment in the Treehouse series, The 52 Storey Treehouse (2014), is fourth best-selling Australian book for first-day sales.
When Griffiths visited Ellenbrook in September last year, he helped Ellenbrook Primary School break a world record.
A human forest of 766 Ellenbrook students, parents and teachers set a new Guinness World Record for the largest gathering of people dressed as trees.