Draw the trees, and then try to partition every node into (left, element, right).

For example, in your first example (Node leaf "msg 1" leaf), we get

Node "msg 1"
├── leaf
└── leaf

In the second example,

Node "msg 1"
├── leaf
└── Node "msg 2"     -- A sub-tree
    ├── leaf
    └── leaf

Now, substituting a leaf with a Node in the above tree will lead to larger trees.
For another example, look here: http://en.wikipedia.org/wiki/Tagged_union#Examples

On 28 February 2015 at 14:10, Roelof Wobben <r.wobben@home.nl> wrote:
Hello,

I found out that for 1 item I can do this : node = Node leaf "msg 1" leaf
And for 2 items I can do this : node = Node leaf "msg1"  (Node leaf "msg2" leaf)

But now I wonder how I can make this work with recursion. It seems that I keep the first 2 items and change the 3th one from leaf to another node

Roelof


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--
Regards

Sumit Sahrawat