Day 1: XY Tree

The next day: (X+5)(Y-5)

Day 3: (X+ 10)(Y- 10)

Day 4: (X+ 15)(Y- 15

)

Day 5 (X+20)(Y-20)

Day 6 (X+25)(Y-25)

Day 7 (X+30)(Y-30

)

therefore

Most kinds of trees