“The Batak peoples of north Sumatra are associated with a distinctive writing culture, with manuscripts written on a range of organic materials, primarily tree bark, bamboo and bone.  Most characteristic are the bark books known as pustaha, written on strips of bark of the alim (Aquilaria malaccensis) tree, which is folded concertina-fashion, and sometime furnished with wooden covers, which can be beautifully decorated.” (Read more.)

Source: Batak manuscripts in the British Library – Asian and African studies blog