A tree is added by capturing a tree type (eucalyptus, maple, teak, etc.), a maturity (mature, seedling, etc.), a unit (hectare, stem, etc.) and a quantity. Should you link a tree to an actual polygonal geometry, then the quantity and unit fields are automatically populated using the polygon’s size. For your information, when using rates for trees, they are based on the combination of type, maturity and unit, and multiplied by the quantity.