Boost Ptree Custom Sort

Hey i want to use this Function and make a custome sorting function. But i dont know how the Compare Function works or with a lambda.

Could someone be so kind to give me a working example for using it.

/** Sorts the direct children of this node according to the predicate. * The predicate is passed the whole pair of key and child. */ template void sort(Compare comp);

The predicate is passed the whole pair of key and child.

Is this a pair of key/ptree ? Dont know how the datatype must be