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.
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READ NOWGriffiths' 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.