**Problem : **
Recall from that it is possible to represent arithmetic, parenthesized
expressions using a tree. If a node is an operator, such as a plus or
a division sign, each of the children must be either a number, or another
expression. In other words, the two children of an operator will be its
operands.
+
3 4
The above means (3+4).
Write a function which will take in a `tree_t` of the form:

`op`field will be one of the following values, '+' '-', '*', '/', or '_', which are sharp defined to be ADD, SUB, MULT, DIV, and EMPTY respectively. Assume that the tree is a well formed expression (you don't need to do any error checking).

**Problem : **
Assume now that your nodes represent people and their ages and as a result
have fields for a person's name and age. Use the following definition for
`tree_t`:

`tree_t`and will free the entire tree and all of the memory associated with it.

**Problem : **
A Huffman tree is a means of encoding characters, that is, a way of
assigning a certain sequence of bits to a character (ASCII is another
convention). The idea is that you can save space when storing a file if
you can find an encoding for the characters such that the file requires
fewer bits overall. We will not cover the process of building such a tree,
but we will consider the process of using one. Starting from the root
node, you keep walking along either the left or the right branch until you
reach the desired character. Moving left corresponds to a 0 bit and moving
right to a 1 bit. So, if you have to go left, right, right to get to the
character 'A', then the encoding for 'A' is 011.
How can you describe the location of all of the nodes that have characters
associated with them? The root node, for example, has no character associated
with it.