Also, of course, your specifications for how the decorations should be added is pretty much non-existent.

Your random tests are testing user function against itself.

Initial code is wrong (has wrong number of arguments).

Needs random test cases

Some questions:

In decoratedTree(7, 2) I suppose 2d argument is for number of o-decoration per "row" (It would be better to tell it explicitely).

• Then why Is there only one o in 4th row of your tree ? :

      @      
      ~      
     ~oo     
    ~~~~o    <-- there !

• What are we supposed to do if this 2d argument is greater than row width (like in 2d row for example) ?

      @      
      ~      <-- no deco ?

• Where are we supposed to put decorations ?

   oo~~~~~    <-- on the left ?
  ~~~oo~~~~   <-- ... the middle ?
 ~~~~~~oo~~~
~~~~~~~~~oo~~ <-- ... the right ?

It seems there're spaces on the right too except the last one . . .

      # <-- here !

• Is it an issue or expected behaviour ?