When a swimmer sees the treetops by the pool, the light reflected by the treetops by the pool is refracted when it hits the water obliquely. At this time, the refraction angle is smaller than the incident angle, and the refracted light approaches the normal line and deflects downward into people's eyes. However, people seem to see the virtual image of the treetops with high actual position against the direction of light.
So, the answer is: virtual; High; Air; Water; Less than.