Witches broom or little leaf disease is a hormone-induced growth distortion of woody plants that only affects part of the plant.
In a prior Foxypress I discussed galls that differ from the strange and miniature witches broom shoots and leaves that are induced by insect spread viruses and phytoplasma (primitive bacteria), or fungal infection.
The image on the left shows a wandoo affected by witch's broom near the Marri picnic area.