code: def getFirstLevel(self) :
  		
  		res = []
  		if len(self.children) > 0 :
  			for c in self.children:
  				res.append((c.x1, c.x2)) 
  		else :
  			if self.x1 != None :
  				res = [(self.x1, self.x2)]
  			else :
  				res = None
  		return res
docs: returns a list of couples (x1, x2) of all the first level indexed regions