Here is the full list of all 11 Bonsai achievements.
Prune lots and lots of branches
Prune lots of branches
Help a tree to grow fully into adulthood
Grow a Sycamore
Grow a Birch
Grow a Japanese Maple
Chop off your trees at the trunk
Grow many different trees
Prune some branches
Grow an Oak
Grow a Sugar Maple