ooooooch, in old towns you also didn’t have more floor area... but sometimes up to 4 stories high. I wonder if that’s possible here?
And if one would even want that?
The OP meant he wants 2 stories plus a basement and underground parking. The problem isn’t just the tree (although without it it would of course be almost easy). The property boundary is also not right-angled. So if you want to use the area, you’d probably have to build an absolutely spectacular something that hardly has any right angles and also a round arch around the tree. Mottenhausen had already hinted at this. I’ll add to that:

[Overview]

[The underground parking garage is also very questionable, especially since in this variant you’d have to swing past the front door, which is really dangerous. For that reason, it would normally go on the ground floor for me. But then the window for the guest would be gone. Well...]

[I would swap kitchen and living room here, but the OP wanted the kitchen in the north.]

Of course, it’s just play-acting, apart from the fact that it would be extremely expensive and we don’t even know what the OP needs.