How to Generate An Expression to A LOL?

[z sway]

the expression only contains number and"+*()"
the form of list is like[op,node1,node2...],op is "+"or"*",node can be a
number or a child list.
e.g :1*2+3*4*(5+6)
      [ '+', ['*', '1', '2'], ['*', '3', '4', ['+','5', '6'] ] ]
Thanks!