Hey Jhapaliketo, I went Nepal this summer. I did not go to Ktm. As your name suggests, I'm assuming that you are from Jhapa and that will be your final destionation in Nepal. My experience is, if you don't have to go to ktm, then the route via Kolkata is quite nice. You can fly from Kolkata to Bagdugra Intl airport  in 1 hr and withing 1 hour from there you are at home. The fare is also  quite cheaper via calcutta route compared to ktm.