XState parallel states

machine.js

const myMachine = Machine({
  id: 'slide',
  initial: 'ground',
  states: {
    ground: {
      on: {
        CLIMB_UP: 'ladder'
      }
    },
    ladder: {
      type: 'parallel',
      states: {
        leftLeg: {
           initial: 'down',
           states:{
             down: {
                on: {
                 LIFT_LEFT_LEG: 'up',
                },
             },
             up: {
               type: 'final'
             }
           }
        },
        rightLeg: {
           initial: 'down',
           states:{
             down: {
                on: {
                 LIFT_RIGHT_LEG: 'up',
                },
             },
             up: {
               type: 'final'
             }
           }
        }
      },
      onDone: 'topOfSlide'
    },
    topOfSlide: {
      on: {
        CLIMB_DOWN: 'ladder',
        SLIDE: 'ground'
      }
    },
  }
})