Preflop trees with many players tend to get very large. It is therefore strongly recommended to build sparse postflop subtrees to reduce computation time and allow less card abstraction. Begin by building the preflop tree, with an empty postflop tree. Save the tree so you can easily revert back and try different postflop settings.
Sparse postflop trees can be created with the following filter. Right-click the root node, choose "Add to all->custom filter."
You should also consider removing preflop options which are not very important, yet bloats the overall tree size, such as flat calls by the small blind.