Don't understand cycle numbers


listing the content of the root file I’ve just produced , I don’t understand why the TTree object T is on file twice with two different cycle numbers (what is a cycle number?) while I have written it only once (tree->Write()).

root [1] f = new TFile(“BuildBeautyPb_1.0.root”)
(class TFile*)0x8bd2908
root [2] .ls
TFile** BuildBeautyPb_1.0.root
TFile* BuildBeautyPb_1.0.root
KEY: TTree T;12 Heavy flavor tree
KEY: TTree T;11 Heavy flavor tree

Any pedagogical explanation?

Many thanks

PS: ROOT Version 4.02/00 + SL3

see TTree::AutoSave … e:AutoSave


in my Root file the cycle numbers are 3, 4 and not 1, 2, 3, 4.
The Root file is suspiciously big.
Could there be an underlying problem?

I also wander at this:

TTree * t = (TTree*) f -> Get(“tree_name”)

t now points to TTree object with the highest cycle number.
Hence when iterating over t I read only a part of the TTree, but I would like to iterate over the entire TTree, containing all cycles.