This is a simple script which take one input argument and creates a file with a tree.

myAnalysis.py

import sys
from ROOT import TFile, TTree, gRandom
from array import array
 
if len(sys.argv)<2:
  print ">>> ERROR! No input arguments given."
  exit(1)
 
print ">>> input = \"%s\""%(sys.argv[1])
name = sys.argv[1]
file = TFile("tree_%s.root"%(name), 'recreate')
tree = TTree("tree_name", "tree title")
px   = array('d',[0])
phi  = array('d',[0])
tree.Branch("px",  px,  'normal/D')
tree.Branch("phi", phi, 'uniform/D')
 
print ">>> filling tree \"%s\""%(tree.GetName())
for i in xrange(10000):
  px[0]  = gRandom.Gaus(20,2)
  phi[0] = gRandom.Uniform(2*3.1416)
  tree.Fill()
 
print ">>> write to file \"%s\""%(file.GetName())
file.Write()
file.Close()
 
print ">>> done"