palantir question - create a tree out of tuples with 2 elements ( data, depth)

palantir.py

'''
Create a tree out of a list of tuples - (data,depth)
Constraint: The new level node should be added to the latest of the old level node
 ex: 
 if the tuple is:
 (a,1)
 (b,2)
 (c,2)
 (d,3)
 (e,2)
 (f,3)
 
 the tree should look like this:
 
    a
  / | \
  b c e
    |  \
    d   f
'''
import sys   
class Node(object):
    def __init__(self,data,depth):
        self.data=data
        self.depth=depth
        self.children = []
    

class Tree(object):
    def __init__(self):
        self.root = None        
        
    def buildTree(self, n):
        if self.root is None:
            self.root = n
            if n.depth > 1:
                sys.exit(1)
            return self
        
        
        if self.root.children is None:
            if (n.depth - 1) != self.root.depth:
                sys.exit(1)
            else:
                #self.root.depth == (n.depth - 1)
                self.root.children.append(n)
        
        current_parent = self.root

        while n.depth > current_parent.depth:
            if n.depth == (current_parent.depth+1):
                current_parent.children.append(n)
                return self

            if current_parent.children:                                
                current_parent = current_parent.children[-1]                              
            

        if n.depth == (current_parent.depth+1):
            current_parent.children.append(n)
        return self

def printTree(root):
    if root is None:
        print 'empty'
    print root.depth
    print root.data
    print '{'
    for i in root.children:
        print i.data
    print '}'


    for i in root.children:
        printTree(i)

    
    
def builder(input):
    T = Tree()
    for i in input:
        print i
        n = Node(i[0],i[1])
        T.buildTree(n)
    printTree(T.root)

#input = [('a',1),('b',2),('c',2),('d',3),('e',2),('f',3)]
input = [('a',1),('b',2),('c',2),('d',3),('e',2),('f',3)]
builder(input)