Does having more bus in the computer increasing speed?
It is difficult to answer in full generality for any kind of bus but I think generally the answer is: no.

First speed is imprecise, there are two notions: latency and throughput. Increasing the width of a bus can increase throughput but it will not help latency. Second, in theory doubling the width indeed doubles the throughput, but there is much to consider than the bus itself. Indeed, the data comes from somewhere (source), is used somewhere else (destination) and will usually travel over several (internal) buses. Thus it is pointless to have a super fast external bus if your CPU and/or internal bus is slow for example. Also if the data comes, for example, from a hard drive then it cannot be read faster than some speed for mechanical reasons and increasing the bus width will not change that. The same applies to the destination: if your CPU cannot process the data fast enough, then having a large bus is also pointless.

Finally, I would like to point out that increasing the width of a bus comes with its own problems, like interference and routing.