The twig is a fork in the tree trunk. One distinguishes according to form between “U- and V-twiggle”.
U-twigs are generally more stable and resilient – as their wood fibres are better interlocked, they are also more suitable as an anchor point for treehouse construction.
With V-twigs, on the other hand, the bark grows into the bifurcation and the fibres are only moderately to not interlocked at all – V-timbers are far less resilient and tend to tear out, so they should not be used as an anchoring point for heavy loads.