Вывести список всех элементов древа в лексикографическом порядке

def set_and_get_h(name, d_par, d_h):
    if d_par[name] == None:
        d_h[name] = 0
    if d_h[name] == None:
        if d_h[ d_par[name] ] != None:
            d_h[name] = 1 + d_h[ d_par[name] ]
        else:
            d_h[name] = 1 + set_and_get_h( d_par[name], d_par, d_h )
    return d_h[name]
#==============================================================================
d_par  = {}
n = int( input('n = ') )
for _ in range(n):
    c, p = input('потомок, родитель: ').split()
    if not p in d_par:
        d_par[p] = None
    d_par[c] = p
d_par = dict( sorted(d_par.items()) )
d_h   = dict.fromkeys(d_par, None)
for name in d_par:
    print( name, set_and_get_h(name, d_par, d_h) )

def get_h(name):
    if name not in tree:
        return 0
    return get_h(tree[name]) + 1
 
 
tree = {}
names = set()
for _ in range(int(input()) - 1):
    child, parent = input().split()
    tree[child] = parent
    names |= {child, parent}
 
for name in sorted(names):
    print(name, get_h(name))