Possible Clues:

• Bush expels one from a spy organisation twice
• Thorny tree, wattle
• Thorny flowering shrub
• Shrub or tree with clusters of white or yellow flowers
• Twice Bill and I get together in a gum tree
• Umbrella-shaped savanna tree
• Australian shrub
• Plant such as the Australian wattle
• Tree of the mimosa family...mmm, mimosas
• Flowering tree or shrub