I'd like to expand on this, if I could.
The way it would be really nifty to be done would be similar to what Sangiusius described, but here's my fleshed out version:
The research tree isn't a tree perse, but more of a list of research possibilities. There would be energy, population, industry, etc. They would be very broad categories that would allow for more specific researching to be done later. Rather than researching one at a time, you could allot a specific amount of research points/turn into each of the categories.
Then, when you have enough points built up in, say energy, you could "buy" an advancement. Say, lasers to begin with. Lasers would cost something like 500 research points in Energy to "buy". But, lasers mark II would only cost 100, with the requirement of having Lasers mark I already researched.
However, if an alien species already has Lasers Mark II, and you've had x number of battles against them, so you are familiar with the concept of lasers mark II, then the advancement cost would be slightly lowered. Or, you could forgo buying lasers mark ii, and save up your research points to completely skip lasers marks ii through v, and jump right into phasers. But, the cost for doing such would be greater than lasers+mark ii+mark iii+mark iv+mark v+phasors (so, if the "base cost" is 500, plus 100 for each level of improvement (for a total of 900 research points to reach lasers mark v, then 500 to research phasors), it would cost you a total of 1000 research points to skip ahead from lasers to phasors, or 1500 to skip from nothing to phasors).
This could also open up avenues of "joint research" with other races. If, for example, you open a joint research alliance with the Thalans, and they have 50 rp going into energy, and you have 50 rp going into energy, then you both have 100 rp going into energy, and you both gain the same achievements at the same time. The risk to this would be, you might be saving your RP to jump five marks to the next new technology, while the Thalans are content upgrading to new marks each time. Then, just as they've reached phasors mark iii, and you're only on lasers mark iii (waiting enough points to skip phasors all together and get disruptors), the Thalan cut off research trade and declare war against you. You're stuck with pea shooters, while they're shredding your ships to bits.
You'd also be unaware of how other races are allocating their research (except for those involved in joint research, or maybe even even narrower, you chose one research field to conduct joint research on, rather than a blanket joint research pact), unless you have spies working in their domains. By allocating spending to the spy network, you could opt to have your spies just monitor what your neighbours are researching, or have them acquire some of the information (for research bonuses, or a chance of getting caught and sparking a war). If you're working on energy with the Thalans, and they've developed Phasors Mark II, your spy can come back and tell you and ask if you want to acquire it. If yes, and successful, you've gained a free research product. If you fail, well, you've got other problems to deal with.