species identification

can anybody please identify this species?

Rudiment - more info and pictures are needed. Check out the instruction post on ID help . I'd be glad to help with some more info

One thing we definitely need is an idea of scale.

I saw you're in Kolkata: this must be a subtropical species then.

I realized that soon enough not to write a stupid thing like "maybe a fraxinus?"...   

Hello Rudiment - as others have already said, there is not enough here to give a reliable opinion as to the identity of your plant. The only guess I can offer at this point is that this seems to be a legume (bean family member). The leaf in your picture seems to be compound and the thickened area just below each leaflet looks like a pulvius (the structure that allows legume leaves to open and close with daylight and/or touch). But given what you have shown here I will not hazard any more of a guess than legume (and there are about 19,000 species of legumes in the world..)

There is one aspect of this tree that transcends a specific ID; it has compound leaves.  Generally speaking, trees with compound leaves do not make for good bonsai.  The only exception I know of would be the Brazilian Rain Tree. Of course I am assuming you are interested in this plant in view of making a bonsai out of it?