Can't see the forest for the trees
Haskell 310 bytes

w i=putStr$unlines$reverse$b i 0 0[][]
b 0 _ _ w r=e w r
b c l 0 w r=b c(l+1)l(e w r)[]
b c l p w r=b(c-1)l(p-1)w(n(++)["  ||    ","  ||    ","///\\\\\\  "," //\\\\   ","  /\\    "]r)
e w r=t++n(n d)(map(\t-&gt;"    "++t)w)c where(t,c)=splitAt 2 r
n f(a:c)(b:d)=f a b:n f c d
n _ a[]=a
n _ _ a=a
d d ' '=d
d _ d=d


Call it with w 5, for example.

Here the uncompressed code:

-- TreeTree
-- by Gerhard
-- 12 February 2017

module TreeTree (wood,test) where

type Tree = [String]

-- Test cases
test = do
 wood 0
 wood 1
 wood 2
 wood 3
 wood 4
 wood 5

-- build wood
wood :: Int -&gt; IO ()
wood i = printTree $ buildWood i 0 0 [] []

-- Prints the trees
printTree :: Tree -&gt; IO ()
printTree = putStr . unlines . reverse

-- build wood
buildWood :: Int -&gt; Int -&gt; Int -&gt; Tree -&gt; Tree -&gt; Tree
buildWood 0 _ _ w r = concatTree w r 
buildWood c l 0 w r = buildWood c (l+1) l (concatTree w r) []
buildWood c l p w r = buildWood (c-1) l (p-1) w (addTree r)

-- indent definition
space :: String
space = "    "

-- tree definition
tree :: Tree
tree = reverse [
 "  /\\    ",
 " //\\\\   ",
 "///\\\\\\  ",
 "  ||    ",
 "  ||    "]

-- Add a Tree on the left side
addTree :: Tree -&gt; Tree
addTree = match (++) tree

-- add tree row at the bottom of the wood
concatTree :: Tree -&gt; Tree -&gt; Tree
concatTree w r = trunk ++ matched
 where
  wood = grow w
  (trunk, crown) = splitAt 2 r 
  matched = matchTree wood crown

-- elnarge forrest on the left side to match next tree line
grow :: Tree -&gt; Tree
grow = map (\t -&gt; space ++ t)

-- match
match :: (a -&gt; a -&gt; a) -&gt; [a] -&gt; [a] -&gt; [a]
match f (a:az) (b:bz) = f a b : match f az bz
match _ a [] = a
match _ _ a  = a

-- match trees
matchTree :: Tree -&gt; Tree -&gt; Tree
matchTree = match matchLine

-- match lines
matchLine :: String -&gt; String -&gt; String
matchLine = match matchChar

-- match chars
matchChar :: Char -&gt; Char -&gt; Char
matchChar c ' ' = c
matchChar _ c   = c

-- End