You can buy heat shrink tape. I'm not keen on electrical tape as the adhesive is nasty slimy stuff to deal with when the tape has been on there for a while. The heat is hard on it in the engine bay combined with fumes etc I reckon it breaks down..
You just wrap the heat shrink tape like normal electrical tape but it has no adhesive. Once you get the the end of the loom or spur you tie it of and then run a heat gun over it. the tape shrinks down tight and seals against itself and makes for a tidy finish. I usually cover this with some of that split flexable conduit. It's available in various sizes to match the size of the buch of wires and provides some mechanical protection to your loom.
The other option for a bit of mechanical protection is spirawrap. It looks OK when applied but is time consuming to wrap.
For loom that runs near hot stuff I then wrap it in aluminum flashing tape. This is self adhesive backed and available from Bunnings. I used this on my land rover for all the wiring that ran near the turbo and exhaust. All the original conduit and tape had been dammaged by the heat and even the wires looked a bit worse for wear. The flashing tape reflects a bit of the heat and should protect the loom underneath.
You can see it here where the
oil pressure sender loom runs past the back of the turbo:
And here where the A/C loom runs near the top of the exhaust mainfold.
I've probably got some spare aluminum tape if you need it.
Cheers