Answer
This graph is not a tree because this graph is not connected.
Work Step by Step
A tree is a graph that is connected and has no circuits. A graph is connected when there is a path between every pair of vertices.
Clearly the graph in this question is not connected. For example, let's consider vertex D and vertex E. There is no path in the graph which connects vertex D and vertex E. Therefore, this graph is not connected.
Since this graph is not connected, this graph is not a tree.
