How can I create a tree for Huffman encoding and decoding?

For my assignment, I am to do a encode and decode for huffman trees. I have a problem creating my tree, and I am stuck.

Don't mind the print statements - they are just for me to test and see what the output is when my function runs.

For the first for loop, I got all the values and index from the text file I used in my main block for testing.

In the second for loop I inserted all the stuff into the priority queue.

I am so stuck about where to go next - I'm trying to make nodes, but I am confused about how to progress. Can someone tell me if I'm doing this right?

def _create_code(self, frequencies):
    '''(HuffmanCoder, sequence(int)) -> NoneType
    iterate over index into the sequence keeping it 256 elements long, '''
    #fix docstring
    p = PriorityQueue()
    print frequencies

    index = 0 
    for value in frequencies:
        if value != 0:
            print value #priority
            print index #elm
            print '-----------'       
        index = index + 1


    for i in range(len(frequencies)):
        if frequencies[i] != 0:
            p.insert(i, frequencies[i])  
            print i,frequencies[i]
            if p.is_empty():
                a = p.get_min()
                b = p.get_min()
                n1 = self.HuffmanNode(None, None, a)
                n2 = self.HuffmanNode(None, None, b)
                print a, b, n1, n2
    while not p.is_empty():
        p.get_min()

I manually inserted the first two to start my tree, is that correct?

How do I keep going? I know the idea of it, just code-wise I am very stuck.

This is using python by the way. I tried looking at Wikipedia, I know the steps, I just need help on code and how I should keep going, thanks!

The HuffmanNode comes from this nested class:

class HuffmanNode(object):

    def __init__(self, left=None, right=None, root=None):
        self.left = left
        self.right =