%%cpp -d
#include "TMVA/DataLoader.h"
#include "TMVA/Factory.h"

#include "TFile.h"
#include "TString.h"
#include "TTree.h"

%%cpp -d
TTree *genTree(Int_t nPoints, Double_t offset, Double_t scale, UInt_t seed = 100)
{
   TRandom rng(seed);
   Double_t x = 0;
   Double_t y = 0;

   TTree *data = new TTree();
   data->Branch("x", &x, "x/D");
   data->Branch("y", &y, "y/D");

   for (Int_t n = 0; n < nPoints; ++n) {
      x = rng.Rndm() * scale;
      y = offset + rng.Rndm() * scale;
      data->Fill();
   }

    Important: Disconnects the tree from the memory locations of x and y.
   data->ResetBranchAddresses();
   return data;
}

TString outputFilename = "out.root";
TFile *outFile = new TFile(outputFilename, "RECREATE");

TTree *signalTree = genTree(1000, 0.0, 2.0, 100);
TTree *backgroundTree = genTree(1000, 1.0, 2.0, 101);

TString factoryOptions = "AnalysisType=Classification";
TMVA::Factory factory{"", outFile, factoryOptions};

TMVA::DataLoader dataloader{"dataset"};

dataloader.AddVariable("x", 'D');
dataloader.AddVariable("y", 'D');

dataloader.AddSignalTree(signalTree, 1.0);
dataloader.AddBackgroundTree(backgroundTree, 1.0);

TCut signalCut = "";
TCut backgroundCut = "";
TString datasetOptions = "SplitMode=Random";
dataloader.PrepareTrainingAndTestTree(signalCut, backgroundCut, datasetOptions);

TString methodOptions = "";
factory.BookMethod(&dataloader, TMVA::Types::kBDT, "BDT", methodOptions);

factory.TrainAllMethods();
factory.TestAllMethods();
factory.EvaluateAllMethods();

outFile->Close();

delete outFile;
delete signalTree;
delete backgroundTree;