let rec display_html (tr:html_tree) =
  match tr with
  |Empty -> failwith("Empty")
  |Html(_, l)-> display_html_list l
  |Head(_,l) -> display_html_list l
  |Body(_,l) -> display_html_list l
  |P(_,l) -> display_html_list l
  |B(_,l) -> display_html_list l
  |I(_,l) -> display_html_list l
  |U(_,l) -> display_html_list l
  |Font(_,l) -> display_html_list l
  |A(_,l)  -> display_html_list l
  |H1(_,l) -> display_html_list l
  |H2(_,l) -> display_html_list l
  |H3(_,l) -> display_html_list l
  |H4(_,l) -> display_html_list l
  |H5(_,l) -> display_html_list l
  |Center(_,l) -> display_html_list l
  |Title(_,l) -> display_html_list state l
  |Word(s)-> (*how to insert strings into a list and go to next iteration*)
let display_html_list (ltr:html_tree list) =
  let rec load stack = function
    | [] -> stack
        | Empty::r -> failwith("Empty")
    | Html(a, l)::r -> load (Html(a,l)::stack) r
    | Head(a,l)::r ->load (Head (a,l):: stack) r
    | Body(a,l)::r -> load (Body (a,l):: stack) r
    | P(a,l)::r -> load (P (a,l):: stack) r
    | B(a,l)::r -> load (B (a,l):: stack) r
    | I(a,l)::r -> load (I (a,l):: stack) r
    | U(a,l)::r -> load (U (a,l):: stack) r
    | Font(a,l)::r -> load (Font (a,l):: stack) r
    | A(a,l)::r -> load  (A (a,l):: stack) r
    | H1(a,l)::r -> load (H1 (a,l):: stack) r
    | H2(a,l)::r -> load (H2 (a,l):: stack) r
    | H3(a,l)::r -> load (H3 (a,l):: stack) r
    | H4(a,l)::r -> load (H4 (a,l):: stack) r
    | H5(a,l)::r -> load (H5 (a,l):: stack) r
    | Center(a,l)::r -> load (Center (a,l):: stack) r
    | Title(a,l)::r -> load (Title (a,l):: stack) r
        | Word(s)::r -> (*how to insert strings into a list and go to next iteration??*)
  in
  match load [] ltr with
    | res :: [] -> res
    | [] -> failwith "no input"
    |_ :: _ -> failwith "remaining nodes"