Huffman tree generated from the exact frequencies in the sentence "this is an example of a huffman tree". It encodes this sentence in 135 bits as "01101010100010111111000101111101000101110001001001001111001111001000111001101

1011110101111010001111101110101110100010111011011000000000", representing about a 53% compression over ASCII's 288 bits, not counting any space for representing the tree. Notice that the frequencies on each level fall between two adjacent powers of 2. The bit pattern and frequency of each character are shown by the table below. Notice that some symbols have different frequencies but the same encoding length; these particularly indicate places where arithmetic coding would do better.
Own work
Dcoetzee