def merge_configs(a, b, copy_trees=False):
        """Merge config b into a

        :param a: target config
        :type a: ConfigTree
        :param b: source config
        :type b: ConfigTree
        :return: merged config a
        """
        for key, value in b.items():
            # if key is in both a and b and both values are dictionary then merge it otherwise override it
            if key in a and isinstance(a[key], ConfigTree) and isinstance(b[key], ConfigTree):
                if copy_trees:
                    a[key] = a[key].copy()
                ConfigTree.merge_configs(a[key], b[key], copy_trees=copy_trees)
            else:
                if isinstance(value, ConfigValues):
                    value.parent = a
                    value.key = key
                    if key in a:
                        value.overriden_value = a[key]
                a[key] = value
                if a.root:
                    if b.root:
                        a.history[key] = a.history.get(key, []) + b.history.get(key, [value])
                    else:
                        a.history[key] = a.history.get(key, []) + [value]

        return a
Merge config b into a

        :param a: target config
        :type a: ConfigTree
        :param b: source config
        :type b: ConfigTree
        :return: merged config a