insert to dictionary using list of keys

def insert(dictionary, tree, value):
    '''it will create key if doesn't exist'''

    for key in tree[:-1]: # without last key
        if key not in dictionary:
            dictionary[key] = {}
        dictionary = dictionary[key]

    dictionary[tree[-1]] = value # last key

def get(dictionary, tree):
    '''it will raise error if key doesn't exist'''

    for key in tree: # without last key
        dictionary = dictionary[key]

    return dictionary # last key

#------------------------------------------------------

usr = {}

comment = 'hello world'
tree = ['acc', 'timeline', 'last_post', 'comments']

insert(usr, tree, comment)
print(usr)

print( get(usr, tree) )