To construct a tree to store Martin, George, Fred and Zubair we add the elements in the order they are given.. So first of all we have Martin.

George is added to the left of Martin as"G" is less than "M".

Fred is added to the left of George. Fred is less than Martin so must be placed on the left. As there is already a node there we must again go to the left.

Zubair is added to the right of Martin as Z is larger than M.

Adding a node to a binary tree following this algorithm -

1. If there is no root the node to add becomes the root.
2. Compare the current node with the node to add
3. If it is smaller we place it to the left, if larger we place it to the right.
4. If a node already exists it will become the current node and we jump to step 2.
5. If there is no node then the node is added