Can glide ratio be increased with bi-wing configuration?
Glide ratio is determined by L/D. If we can increase lift without increasing drag, or decrease drag without decreasing lift, we have a better glide ratio.

Increasing the wing span (for a given wing area => reduce the chord) helps: the longer wing span spreads out the lift creation over a longer distance, thereby decreasing induced drag. Keeping the flow laminar for as long as possible also helps.

Your question is about adding a second wing to an airplane. The problem with biplanes is that they were mainly constructed decades ago, and we associate them with older construction methods and mainly lots of drag, such as addressed in this question. It seems that the classical biplane has no aerodynamic advantages, and always has a lower L/D ratio than a comparable mono wing.

However there are now Computed Fluid Dynamics. There has been work done on biplane configuration with low drag in recent years - many are behind a pay wall, this one is not. Their work found two configurations with high L/D ratios:




Upper wing AoA = 13º
Upper wing forward sweep = 30º
Lower wing AoA = -2.8º
Lower wing backward sweep = 3.5º
Wing profile of both wings = NACA 4412
Both wings 6 ft span and 6 inch chord
Computed L/D = 32.3


The other configuration they found with a high L/D was a canard configuration: one wing in front of the other. If you insist on using two wings, this may be your best bet: one wing mounted in front of the other, in such a way that the back wing is out of the way of the wake of the front wing, or mounted at the optimum AoA for the disturbed flow. Their canard configuration used two different wings, resulting in an L/D of 35.8:



Note that none of the configurations included a fuselage of any kind, so their CFD work would have to be repeated with the fuselage and with interference computations. Fortunately computing power has increased dramatically in recent years.