Buggy python submission (verdict: Time Limit Exceeded):
from __future__ import print_function
from sys import stdin
class Node:
    def __init__(self, id):
        self.id = id
        self.left = None
        self.right = None
        self.parent = None

def preorder_tree_walk(root):
    print('', root.id, end='')
    if root.left != None:
        preorder_tree_walk(root.left)
    if root.right != None:
        preorder_tree_walk(root.right)

def inorder_tree_walk(root):
    if root.left != None:
        inorder_tree_walk(root.left)
    print('', root.id, end='')
    if root.right != None:
        inorder_tree_walk(root.right)

def insert(root, z):
    y = None
    x = root
    while isinstance(x, Node):
        y = x
        if z.id < x.id:
            x = x.left
        else:
            x = x.right
    z.parent = y

    if y == None:
        root = z
    elif z.id < y.id:
        y.left = z
    else:
        y.right = z
    return root

def find(root, x):
    if root.id == x:
        return True

    if root.id > x:
        if root.left == None:
            return False
        else:
            return find(root.left, x)
    else:
        if root.right == None:
            return False
        else:
            return find(root.right, x)

n = int(raw_input())
root = None
for i in xrange(n):
    cmd = stdin.readline()
    if cmd.startswith('i'):
        num = int(cmd[7:])
        root = insert(root, Node(num))
    elif cmd.startswith('p'):
        inorder_tree_walk(root)
        print()
        preorder_tree_walk(root)
        print()
    else:
        # find
        num = int(cmd[5:])
        if find(root, num):
            print('yes')
        else:
            print('no')

Fixed submission:
from __future__ import print_function
from sys import stdin
class Node:
    def __init__(self, id):
        self.id = id
        self.left = None
        self.right = None
        self.parent = None

def preorder_tree_walk(root):
    print('', root.id, end='')
    if root.left != None:
        preorder_tree_walk(root.left)
    if root.right != None:
        preorder_tree_walk(root.right)

def inorder_tree_walk(root):
    if root.left != None:
        inorder_tree_walk(root.left)
    print('', root.id, end='')
    if root.right != None:
        inorder_tree_walk(root.right)

def insert(root, z):
    y = None
    x = root
    while isinstance(x, Node):
        y = x
        if z.id < x.id:
            x = x.left
        else:
            x = x.right
    z.parent = y

    if y == None:
        root = z
    elif z.id < y.id:
        y.left = z
    else:
        y.right = z
    return root

def find(root, x):
    while root != None and x != root.id:
        if x < root.id:
            root = root.left
        else:
            root = root.right
    return root


n = int(raw_input())
root = None
for i in xrange(n):
    cmd = stdin.readline()
    if cmd.startswith('i'):
        num = int(cmd[7:])
        root = insert(root, Node(num))
    elif cmd.startswith('p'):
        inorder_tree_walk(root)
        print()
        preorder_tree_walk(root)
        print()
    else:
        # find
        num = int(cmd[5:])
        if find(root, num) != None:
            print('yes')
        else:
            print('no')