What kind of wood were using the Macedonians when making the sarissa pikes?

The sarissa haft was almost certainly ash. Ash was generally the preferred wood for spear hafts in Europe, and "ash" was a common poetic term for "spear", in at least Old English, Old Norse, and Welsh. Ash appears in ancient literature, for example, in Homer. (Thus, "ash" is the answer to the second part of your question.) Ash was the universally-recommended wood for pike hafts in late Medieval and Early Modern times, because it is (a) strong, (b) light, and (c) grows long enough to make pikes from. Shorter spears are less demanding of the wood used, but ash was still preferred.

However, there is only one known mention of the wood used for sarissa hafts in literature. While the wood mentioned is indeed ash, the source is poetic and can't be assumed reliable, since the same poet write about bark shields. The poet, Statius (1st century AD) wrote:

fraxineas Macetum vibrant de more sarisas

or the "Macedonians by custom shake ash sarissai".

A significant number of descriptions of the sarissa state that it was made of cornel wood. This is based on a passage in Theophrastus which actually says cornel can't be used:

The wood of the "male" tree has no heart, but is hard throughout, like horn in closeness and strength; whereas that of the "female" tree has heart-wood and is softer and goes into holes; wherefore it is useless for javelins. The height of the "male" tree is at most twelve cubits, the length of the longest sarissa, the stem up to the point where it divides not being very tall.

First, this states that the wood of the "female" tree is not even suitable for javelins (implying that the "male" is OK for javelins). Second, this states that the wood isn't long enough - the entire tree only grows to the a height equal to the length of a sarissa, and the straight section of the trunk (which is what would be used for hafts) is much shorter.

As for how, the usual methods were split timber, coppiced poles, and saplings. Coppicing is when trees are pruned near the ground to encourage the growth of long straight new shoots:

https://commons.wikimedia.org/wiki/File:Coppice2.png

which provides a renewable source of hafts. The coppiced pole or sapling can be debarked, and any small branches or lumps shaved off with a draw knife or plane, and the haft can be sanded if desired. Both coppiced poles and saplings are usually tapered, which is often taken advantage of. Tapering is especially important for pikes, since the haft should be thinner toward the head to reduce weight and stop the pike from sagging under its own weight. (Similar, pike heads are usually quite small - the longer the spear haft, the smaller the head.)

For splitting, you start with a section of trunk, straight and long enough. You split it with wedges and/or a froe into pieces a little wider than the desired haft diameter. You can get many hafts from the one trunk (you can also get more than one from a sapling or coppiced pole if it's wide enough). Splitting is much better than sawing because it ensures that the grain of the wood was continuous along each piece - this is important for getting maximum strength with minimum weight. The split pieces are rounded using a draw knife.

If required, the hafts (however they are made) could be straightened, using either dry heat or steaming to make them bendable. One example of straightening spear hafts with very simple technology:

https://www.youtube.com/watch?v=RuGwQ2FByuY