// k2 semi-recursive

/ paths to leaves (recursive)
pl:{{:[5=4:y;,/(x,/:!y)_f'y[];,x]}[();x]}

/ subtree where leaf x is f x (non-recursive)
st:{[t;f]               / subtree of t where leaves are f
 p:pl t                 / paths to leaves
 d:t ./:p               / data at leaves
 i:&f d                 / where leaves are f
 ./[.();p i;:;d i]}     / subtree

/ pretty-print (recursive)
pp:{`0:{:[5=4:y;,/(x$!y){(,x),y}'(1+x)_f'y[];,(1+x)$y]}[1;x]}

\

/ tree
  t[`a;`b`c`d;`e`f]:3 2_draw 100

/ print t
  pp t
a
 b
  e 31
  f 51
 c
  e 29
  f 35
 d
  e 17
  f 89

/ subtree where 50<leaf
  s:st[t;50<]

/ print s
  pp s
a
 b
  f 51
 d
  f 89

/ alternative pretty-print (non-recursive)
pp:{
 p:pl x
 q:?,/((1+!#:)'p)#\:'p
 d:x ./:p
 d:@[(#q)#0N+*0#d;&q _lin p;:;d]
 `0:{(x$z)," ",$y}'[#:'q;d;,/-1#'q]}