ruby_tracer.rb

# the code

def method_i_want_to_trace
  method_a
  method_b
end

def method_a
  method_a1
  method_a2
end

def method_b
  method_b1
  method_b2
end

def method_a1; end
def method_a2; end

def method_b1; end
def method_b2; end

# the output (trace)

           method_i_want_to_trace
           /                    \ 
       method_a              method_b
        /   \               /     \
method_a1  method_a2  method_b1  method_b2