Treant

Treants are a race of large, roughly humanoid tree-people. When one stands still with its legs together it cannot be easily distinguished from a normal oak tree. Their leaves are nearly identical to oak leaves, and are green in spring and summer, turning orange, red, or yellow in the fall and winter. A treant's leaves do not normally fall out in the winter, but as some oaks also retain their leaves into cold weather this may not help in identifying one.
  Being actual trees, treants are big, averaging 25 to 35 feet in height and weighing 4,000 to 5,000 pounds. Their language is difficult for most other races to learn, though Elves are known to have an advantage in mastering it. Many treants know Elvish, and some who live near humans learn Common as well.