Your first homework is the following question.
Due date is: Wednesday 1st, March

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Write a function subtree  which receives two TERNARY trees and return true
if the first tree is a subtree of the second, or false otherwise.
(In trees the structure is important, thus a tree could be a subtree in
any place).

You will use the following datatype.

- datatype tree = Empty |
                  Leaf of int |
                  Node of int*tree*tree*tree;
                  
- val tree1 = Node(3,Leaf(5),
                     Node(6,Leaf(7),Leaf(4),Empty),
                     Empty);
                     
        3            
       / \           
      5   6          
         / \         
        7   4        
        
        
- val tree2 = Node(13,Node(3,Leaf(5),
                             Node(6,Node (7, Leaf (2), Empty,Empty),
                                    Leaf(1), 
                                    Node(4,Leaf(3),Leaf(4),Leaf(1))),
                             Empty),
                       Leaf(1),
                       Node(12,Leaf(9),
                               Node(6,Leaf(11),Leaf(7),Leaf(4)),
                               Empty));
                               
                               
           13                  
         /  | \                
        3   1  12              
       / \     / \             
      5   6   9   6            
         /|\     /|\           
        7 1 4  11 7 4          
       /   /|\ 
      2   3 4 1

- subtree(tree1,tree2);
> true