Growing up your tree to make it have more limbs, building weapons on limbs or trunk to defense the insects, killing them to earn water.
Insects come from the insect holes, they will only attack the trunk, your weapons will not fire on insects once they've already landed on the trunk of the tree, so you'll have to build weapons to defend the trunk while they're still in the air.
Buy/Upgrade more weapons when you get points, you can plan different strategies with different weapons.
Mouse wheel to scale the scene, Mouse drag to move the viewport;
Hotkeys: Spacebar to select the trunk, Shift to switch between fast mode and normal mode, P to pause.