Does insulin deficiency lead to high glucose level?

Both insulin deficiency AND insulin resistance lead to high glucose levels.

In type 1 diabetes mellitus, there's an insulin deficiency as the beta cells (islets of Langerhans) in the pancreas that produce insulin are destroyed by the body's own immune system.

In type 2 diabetes mellitus, the body's cells become resistant to the effects of insulin, meaning that glucose in the bloodstream can not be used by the body's cells to make energy.

Diabetes mellitus is the predominant cause of high glucose levels.

In theory yes, insulin processes sugar/glucost and metabolisis them, so less insulin = more glucose.

Well, with no insulin the glucose can't go from your blood into your body's cells so it just sits there in the blood. So... yeah. Insulin deficiency can be caused by type 1 diabetes (not type 2).

Hope I helped :)