The first large node 54- K binary search tree

Title: Given a binary search tree, find the first of the big K nodes.

def inorder(head,res):
    p = head
    if p:
        inorder(p.left,res)
        res.append(p.data)
        inorder(p.right,res)

def tree_k(head,k):
    res = []
    inorder(head, res)
    return res[k-1]

　　NOTE: The preorder, taken out after the completion of the K-th traversal. The official program is given direct access to the K-th node to stop now do not understand, the latter will be optimized.