#include <TFile.h>
#include <TTree.h>
#include <random>

void gen_tree()
{
    std::random_device rnd;
    std::mt19937 mt(rnd());
    std::normal_distribution<> norm(10, 1);
    auto fileName = "test.root",
         treeName = "tree";
    auto f = new TFile(fileName, "recreate");
    auto tree = new TTree("tree", "tree");
    double x;
    tree->Branch("x", &x, "x/D");
    for (int i = 0; i < 1000000; ++i)
    {
        x = norm(mt);
        tree->Fill();
    }
    tree->Write();
    f->Close();
}