Accessing Boolean values by parsing JSON file using boost property tree

Below are the steps i followed to fetch the values from the json file. And i am failing to fetch the boolean values from the json file.

Input Json:

 {"Bases":[{"mnemonic":"ADIS.LA.01","relay":true},{"mnemonic":"ALEX.LA.01",,"relay":true}]}

In the code below Iam

1. Opening the json file
2. Set the root element and start travering the childtree under this root element(Bases)
3. Fetch the values of each tag and save it to appropriate variable type

Code:

 ReadJsonFile()
 {
    using boost::property_tree::ptree;
    const boost::property_tree::ptree& propTree
    boost::property_tree::read_json(ss, pt);
    const std::string rootElement = "Bases"; 
    boost::property_tree::ptree childTree;
    bool m_relay;
    try
    {
        /** get_child - Get the child at the given path, or throw @c ptree_bad_path. */
        childTree = propTree.get_child(rootElement);
    }
    catch (boost::property_tree::ptree_bad_path& ex)
    {
        return false;
    }

    BOOST_FOREACH(const boost::property_tree::ptree::value_type &v, propTree.get_child(rootElement)){
       string vID;
       for (ptree::const_iterator subTreeIt = v.second.begin(); subTreeIt != v.second.end(); ++subTreeIt) {
          if (subTreeIt->first == "mnemonic")
          {
             // Get the value string and trim the extra spaces, if any
             vID = boost::algorithm::trim_copy( subTreeIt->second.data() );
          }
          if (subTreeIt->first == "relay")
          {
            m_relay = boost::algorithm::trim_copy(subTreeIt->second.data());
          }
       }
    }
 }

Error:

error: cannot convert ‘std::basic_string, std::allocator >’ to ‘bool’ in assignment

Apparently the json file has a boolean value set to the tag "relay":true and the above code treats it as a string but not bool

If i change bool m_relay; to std::string m_relay; The code works fine, but bool type is failing to compile. Am i missing on something? Please advice .

Thanks