Why are tree shadows from a directional light blocky with unity pro?

The tree is the default big tree included with Unity and the shadows are hard shadows being cast onto terrain. The blocky shadows (as in the shadow is not the same shape as the tree but is instead a bunch of large squares with a trunk) look like they are caused because the renderer isn’t taking into account the transparency of leaves when casting shadows. How can I fix this?

This is caused by low quality shadows, increasing Edit/Project Settings/Quality/Shadow Cascades to 4 and other shadow related stuff helps.

For me also in DirectX11 Unity thought it had only 32MB VRAM left so by default it crippled the shadows into the blocky look(or turned them off completely at random). Trying to switch off DX11 helped me to resolve the VRAM detection issues and the shadows display nicely now.