And this is what I came up with.
The weirwood is a species of deciduous trees found all over Westeros. The five-pointed leaves and the sap of weirwoods are blood-red, while the smooth bark on their wide trunks and wood are bone white. Most weirwoods have faces carved into their trunks. This was done by the children of the forest in ancient days, and is now done by the free folk as well as other descendants of the First Men, such as followers of the old gods in the Seven Kingdoms praying to heart trees in godswoods. In some cases sap has collected in the crevices of the carved faces, giving the trees red eyes which have been known to drip sap as if the trees were weeping. - A Wiki of Ice and Fire