The half square triangle unit is probably the most commonly used patch in a quilt block -- well it is second only to the square. It is made simply with two triangles, filling up half the square each -- hence the name. Take a quick look through this website, or in any quilting magazine, and you will start to notice that this half square triangle, regardless of its size, is present in more quilts than not.
Tree of Life
Free Quilt Block Pattern
The Tree of Life is an old and well known quilt block, but you don't see it frequently. I imagine this is because of the number of pieces in the block, but really, there is nothing difficult here - squares, rectangles and half square triangles are the only patches used in this block. The only consideration is to be precise when sewing your quarter inch seam allowance so that there is no difficulty in matching the seams of the various patches.
All that being said, I had fun designing the sample quilt layouts illustrated. By using rotations of the block you can make any number of interesting settings, which create secondary patterns. Depending on what colours you use for your blocks (I only used green and brown because of the name of the block), you will create many striking designs of your own.