$.$

$$A common use for trees is the Expression Tree. This is a specific case of a binary tree. When you write an equation, the computer stores the equation in a tree

$$

$$which stores both the operations and the expression order.

We will give an example

$2$

$$

$3$

$*$

$4$

$+$

$5$

If we traverse the tree using left

$$

$$first traversal

$$

$$the first dead end node is

$2$

$,$

$$then traverse back up to

$$

$$and down to

$*$

$$and then down again to

$3$

$,$

$$then up to

$*$

$$and back down to

$4$

$$

$$so the traversal order without intermediate points is