Rock and trees are the same and different... the basics apply to both equally well, the ropework is completely different. Get 'The Tree Climber's Companion' by Jepson/Kotwicka for ideas about lifelines and ascending.
Off the bat here's a couple things you'll see as you read on this site that it helps to know...
Drt - Double Rope Technique - You can split hairs but most of the time it means climbing with one rope doubled down from a high crotch in the tree (sort of like a top-rope) with an end tied to your harness while the other leg is is attached to your harness by a bridge (split-tail) and a friction knot similar to a Prussik... it forms a closed loop. You self belay by keeping the slack out of the loop using the friction knot.
Srt - Single Rope Technique - Also one rope which is fixed over a high croth in the tree, mainly for ascent and descent... most Srt climbers switch to Drt after ascending because it's works better for positioning. Srt is faster on the ascent in most cases because the single line is fixed.
Lanyard (flipline) - A section of rope attached to the side D ring on your harness with an adjuster (prussik or mechanical rope grab) attached to a second connector you attached to the D ring on the other side... used as another way to secure yourself to the tree... gotta have one.
Spikes - you know what they are, what's important is, if you care about protecting a tree's health, don't use'm on that tree... if you're gonna cut the tree down, they make climbing and positioning easier and more secure... to most folks.
Those are the things I had a hard time figuring out when I first came here, so I thought it was worth mentioning.
If you're a rock climber, you're gonna love tree climbing.
