What makes this visual puzzle so challenging is that the face may not have a clear outline. Your brain recognizes the trees individually, making it difficult to combine their shapes into something familiar. Once you change your perspective, however, the scattered branches and shadows may begin to resemble recognizable facial features.
If you still cannot find the hidden face, slowly scan the entire image from top to bottom. Look for shapes that might suggest the eyes, nose, and mouth, and avoid focusing too much on one particular area. The key is to observe the forest as a whole rather than as a collection of separate trees. Sometimes, the most surprising details are the ones hiding in plain sight.