improve parse part and the way of printing tree

wwwwwyy:Walley0.1 shd101wyy$ ./walley parse "3/4/5"
Begin to Analyze 3/4/5
num:|3|:0:1
m_operator:|/|:1:2
num:|4|:2:3
m_operator:|/|:3:4
num:|5|:4:5
(expr (/ (s_term (/ (3 )(4 )))(5 )))wwwwwyy:Walley0.1 shd101wyy$

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wwwwwyy:Walley0.1 shd101wyy$ ./walley parse "6*(3+4)"
Begin to Analyze 6*(3+4)
num:|6|:0:1
m_operator:|*|:1:2
(:|(|:2:3
num:|3|:3:4
m_operator:|+|:4:5
num:|4|:5:6
):|)|:6:7
(expr (* (6 )(factor (expr (+ (3 )(4 ))))))