The level
is in node vm in 1.0.*. It has been moved into node since 2.0.0. You may use it in the slot like following:
Tree
div(slot-scope="{data, store, level}") {{level}}
Change to:
Tree
div(slot-scope="{data, store}") {{data.level}}
Tree
div(slot-scope="{data, store}") {{data.level}}
Change to:
Tree
div(slot-scope="{data, store, vm}") {{vm.level}}