1. In an ecosystem dominated by trees, the pyramid (of numbers) is _________ type. How is it inverted ? Can't it be spindle shaped too?

2.Which one of the following has the largest population in a food chain? shouldnt it be producers as decomposers are not included in the food chain?.

Pyramid of numbers is inverted for a parasitic food chain of a tree. Tree is the source of food for many herbivore birds and there are many ectoparasites which feed on these birds. So the number increases at each higher level and this forms an inverted pyramid. 

In other case when a tree provides food to many herbivore birds and these herbivore birds are fed upon by few carnivorous birds, it forms a spindle shaped pyramid as the number increases from the first to second level but decreases again at the third level. 

The answer would be decomposers as it includes micro-organisms such as bacteria and fungi. They form the largest population in a food chain and obtain nutrients by breaking down the remains of dead plants and animals. If the food chain includes decomposers then it would have the highest number.