Leetcode 729

class Book:
    def __init__(self, start, end):
        self.start = start
        self.end = end
        self.left = None
        self.right = None

    # check if it can add item as a child to current node
    # return bool
    def insert(self, item):
        if item.start >= self.end:
            # insert to the right
            if not self.right:
                self.right = item
                return True
            return self.right.insert(item) 
        elif item.end <= self.start:
            # insert to the left
            if not self.left:
                self.left = item
                return True
            return self.left.insert(item) 
        else:
            return False

class MyCalendar(object):
    def __init__(self):
        self.root = None

    def book(self, start, end):
        new_book = Book(start, end)
        if not self.root:
            self.root = new_book
            return True

        return self.root.insert(new_book)