It seemed that my effort can never meet my goal. I also tried Visio, and it didn't work well. So I came back to Latex and need advice from you guys. Thank you so much.
The branches are not orthogonal as yours. Could you give me a hint or more information? Still one more question, can this 'tree diagram' be saved as a figure or which form should it appear in my work so I can reference it any where?
@ js bibra I think I found what's wrong with my tex code. In the preamble, before the line
I accidentally added the following line (which could happened any time before I post this question and was looking for a solution on line)
Everything is OK if I remove this line. Thank you so much again @js bibra.