Most people who get this wrong do so because they picture theft as somebody running off with a thing. The Principle does not say that. Its operative words are "moves that property with an intention to take it". Moving is the act it punishes. Getting away with the goods is not mentioned anywhere in the definition, so it cannot be a requirement.
Now think about the tree. While its roots are in Z's soil it is attached to the land, and attached things are not movable property. Cutting it changes that in an instant. The severance turns the tree into movable property and, in the same stroke, moves it. So the moment the axe finishes its work, every ingredient lines up at once: dishonest intention (the facts give it to us), movable property (created by the cut), in Z's possession (it stood on Z's ground), without Z's consent (the facts say so), and moved with intention to take it (the cut itself). The offence was finished right there, on Z's ground, with the tree still lying where it fell.
Let's summarize:
The answer is option (A).