Preheat the oven to 400°F. Slice the top off the head of garlic, drizzle with a little olive oil, wrap in foil, and roast for 30 minutes until soft.
Squeeze the roasted garlic cloves into a food processor. Add the chickpeas, tahini, 2 tablespoons olive oil, lemon juice, salt, and cumin. Blend until smooth, adding a splash of water if needed to reach a creamy consistency.
Cut the broccoli, carrots, celery, cucumber, and red bell pepper as listed.
Spread the hummus in the center of a large platter. Arrange the broccoli florets upright around the hummus to form tree shapes, then place the carrot sticks, celery sticks, cucumber slices, and red bell pepper strips in clusters to complete the forest layout. Drizzle extra olive oil over the hummus before serving.