q2.js

let obj = { 'A': 1, 'B.A': 2, 'B.B': 3, 'CC.D.E': 4, 'CC.D.F': 5}

function split(obj) {
    for (let [key, value] of Object.entries(obj)) {
        nks = key.split('.');
        if (nks.length > 1) {
            nk = nks.shift();
            obj[nk] = obj[nk] || {};
            obj[nk][nks.join('.')] = value;
            delete obj[key];
            split(obj[nk]);
        }
    }
}

split(obj)
console.log(obj);

q2.py

dict = { 'A': 1, 'B.A': 2, 'B.B': 3, 'CC.D.E': 4, 'CC.D.F': 5}

from copy import deepcopy as dc

def split(dict):
    tmp = dc(dict)
    for k, v in tmp.items():
        nks = k.split('.')
        if len(nks) > 1:
            nk = nks.pop(0)
            dict[nk] = dict[nk] if nk in dict else {}
            dict[nk]['.'.join(nks)] = v
            del dict[k]
            split(dict[nk])

split(dict)

print(dict)