Convert Sorted array to BST

class Solution(object):
    def sortedArrayToBST(self, arr):
        def convert(arr,s,e):
            if s>e:return None
            m=(s+e)>>1
            t=TreeNode(arr[m])
            t.left=convert(arr,s,m-1)
            t.right=convert(arr,m+1,e)
            return t
        return convert(arr,0,len(arr)-1)