I have a Huge XML File of which I want to read its childtrees into the C++ boost::property_tree::pTree type

Question

The normal way of doing it is using

boost::property_tree::ptree pt1;
boost::property_tree::read_xml( XML_FILE_PATH, pt1  );

But what this does is that it reads the entire XML File, which is really huge in the pt1

So I think it is inefficient when we just want to read a childTree.

There is another overload function for read_xml which takes in the File Type istream but I don't know how to work with to solve this

boost::property_tree::read_xml( iStream, pt1  );

Thanks