Maybe something like this:

block-beta
  block:s1
    columns 1
    t1["Stack 1"]
    n1("Node 1")
    n2("Node 2")
  end
  space
  block:s2
    columns 1
    t2["Stack 2"]
    n3("Node 3")
    n4("Node 4")
  end
  s1 --> s2
  style t1 fill:none,stroke-width:0px
  style t2 fill:none,stroke-width:0px

Two stacks