How can i derive fundamental and harmonic form from this fourier transform result?

Hi. I did fourier transform but only i can get is the graph of transformation.

I have to get the fundatmental + harmonic form of given function..how can i get it?

data = csvread('data.csv',1);
t = data(:,1);
x = data(:,2);
ts=0.00005;
fs=1/ts;
N=length(x);
k=-N/2:N/2-1;
f=fs*k/N;
X=fft(x,N);
figure
subplot(2,1,1)
plot(t,x);
xlabel('Time')
ylabel('Amplitute')
title('before')
grid on

subplot(2,1,2)
plot(f,abs(fftshift(X))/N);
xlabel('Frequency')
ylabel('Amplitute')
title('after')
grid on