Looks like your template hasn't a so called "Breadcrumb" position which displays what you call the links tree.
Normally Ninjaboard automatically installs the module Breadcrumb even if it's not activated or installed elsewhere.
Otherwise try to install the module Breadcrumb via the Module Manager and assign it to the breadcrumb position, if there is a breadcrumb position available. You will discover this soon enough if you can or can't choose it from the Positions dropdown menu within the module's settings.
I hope this helps,
Let us know how it goes.