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


class BST:
    def __init__(self):
        self.root = None

    def insert(self, value):
        self.root = self._insert(self.root, value)

    def _insert(self, node, value):
        if node is None:
            return Node(value)
        if value < node.value:
            node.left = self._insert(node.left, value)
        elif value > node.value:
            node.right = self._insert(node.right, value)
        # equal values are ignored - no duplicates
        return node

    def search(self, value):
        return self._search(self.root, value)

    def _search(self, node, value):
        if node is None:
            return False
        if value == node.value:
            return True
        if value < node.value:
            return self._search(node.left, value)
        return self._search(node.right, value)


tree = BST()
for n in [8, 3, 10, 1, 6, 14, 4, 7, 13]:
    tree.insert(n)

print(tree.search(6))    # True
print(tree.search(11))   # False