Simple binary tree in python with pre-order search

binary_tree.py

class Node(object):
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None

class BinaryTree(object):
    def __init__(self, root):
        self.root = Node(root)

    def search(self, find_val):
        return self.preorder_search(self.root, find_val)

    def print_tree(self):
        return '-'.join([str(i) for i in self.preorder_print(self.root, [])])

    def preorder_search(self, start, find_val):
        if start == None: return False
        if start.value == find_val: return True
        return self.preorder_search(start.left, find_val) or self.preorder_search(start.right, find_val)

    def preorder_print(self, start, traversal):
        if start == None: return traversal
        traversal.append(start.value)
        self.preorder_print(start.left, traversal)
        self.preorder_print(start.right, traversal)
        return traversal