After "The Oak Tree" has been published in Chapter 6, Orlando is at loose ends. Random memories start floating up in her mind, and she can't keep track of their sequence. While she was still working on "The Oak Tree," there was an order to the novel that arose from the need to get Orlando's character from unsuccessful male writer to successful woman writer. Once "The Oak Tree" has been published, that linear narrative ends. We are left with Orlando's disordered memories and reflections. For Woolf, individual memory is episodic and random. What imposes order on memory is the process of writing a narrative. The past only takes on a linear structure in retrospect, when you're constructing a story from it.
As Orlando progresses, memory and the past occupies a greater place in the narrative, whereas before the emphasis had been on action.
By finishing "The Oak Tree" and turning her house into a museum, Orlando severs the closest connections she has with her past.