Access data from a Tree

Hello Everybody,
I am Nhat, I am a new member.
I start learning root recently, I had some problems with trees. i could not solve it.
i hope everybody can help me solve it.
My problem is
my purpose: I want to draw 2 PPAC,tPPAC histograms, and fit “gaus” for each.
but my code had a problem.
Below are the link code and file root I want to analyze.

image

My code : nhat6.C (1.2 KB) .

My root file is big, so you can download it here: [run01.root - Google Drive]

(run01.root - Google Drive)