Tree seeds can be stone fruit cores or pomaceous fruit seeds, and both often require special treatment in order to be capable of germinating, because they have a hard and waterproof shell. In addition, usually a cold stratification is necessary, as in their natural habitats tree seeds rest over the winter, before they germinate and sprout the next year.
Especially nut trees, all kinds of non-grafted fruit trees, shrubs and hedges are excellent candidates for growing from seeds.