Well that depends on the thickness of the tree, doesn't it?
And of course, if it is a bendable tree =P
I use the makiwara, maybe not 100 times a day, but it gives results and kime anyvay. If it's traditional karate you are praticing, kime is what you need. And for that, you need the makiwara =) But the heavybag is good too, as it simulates a human body much better than the makiwara.
Iv'e heard that you shouldn't attach the makiwara on the wall, because if you hit the makiwara too hard when it's attached to the wall, you could break your hand.
Here's a link to a site that has some stuff about the makiwara:http://www.ctr.usf.edu/shotokan/makiwara.html