Purple Hibiscus is not a bildungsroman as the main protagonist Kambili is still a child from start to finish. A bildungsroman is only that in which a character experiences moral or educational growth that starts from childhood and finishes at adulthood. Something like Mill on the Floss, Great Expectations or Jane Eyre is more suited to be a bildungsroman novel.
What is a real good and popular A-level bidungsroman is Atonement by Ian McEwan (2001). It's a heavy novel, but in my opinion so worth it!