There will be a number of trees, including the central sitting area, beside the pond, in the orchard forest garden, and scattered around in other places where they will fit. Lemon trees are particularly easy to place because they can often be grown as a shrub, rather than a full size tree.
If you are speaking about the tree in the central sitting area, I had a magnolia in mind. It is ever-green, has big beautiful flowers, a nice canopy, and is representative of the place I live.