如何从XML数据构建含指定4列的Pandas DataFrame？

我想要创建一个Pandas DataFrame，让每个城市对应其所属国家，最终DataFrame需要包含4列：Country、City、ImrByCountry、PopulationByCity，而非当前输出的3列（Country、IMRperCountry、PopulationByCountry）。我写了下面的代码，但把生成的字典转换成DataFrame时没能成功：

import pandas as pd

data = {}

for country in root.findall("country"):
    country_name = country[0].text
    imr = country.findtext('infant_mortality')
    population = country.findtext("./population[@year='2011']")

    cities_in_country = {}

    for city in country.findall("city"):
        city_name = city[0].text
        city_population = city.findtext("./population[@year='2011']")
        cities_in_country[city_name] = city_population

    data[country_name] = {
        'IMR': imr,
        'Population': population,
        'City': cities_in_country
    }

内容的提问来源于stack exchange，提问作者Radion Nazmiev