What is the difference between HashSet and TreeSet ?

• The HashSet is Implemented using a hash table.
• Its elements are not ordered. 
• The add, remove, and contains methods of a HashSet.
• Time  complexity O(1). 

•  TreeSet is implemented using a tree structure. 
• The elements in a TreeSet are sorted.
• The add, remove, and contains methods.
• Time complexity  O(logn).