Steps to repro:

1. Open attached project (see owncloud link in the comment) and 'TreeOcclusionBug' scene;
2. Double-click on Main Camera gameobject;
3. Set some value (around 100) to Field of View field of Camera's Inspector;
4. Save scene by pressing Ctrl+S shortcut;
5. Switch to Occlusion tab in Editor;
6. In Editor's Occlusion tab enable 'Portals' by ticking corresponding checkbox;
7. Switch back to Inspector tab.

Expected result:
Inspector tab is visible and Editor doesn't crash.

Actual result:
Editor crashes.

Regression introduced in Unity 2017.2.0.
See attached video for clarity.

Following callstack is displayed in Editor.log:

0x0000000141DEEFFA (Unity) memcpy
0x00000001412ADB3A (Unity) dynamic_array<unsigned char * __ptr64,8>::erase
0x0000000141A8825A (Unity) TerrainRenderer::GetPatchVertexStream
0x0000000141A8B93C (Unity) QuadTreeNode::PrepareBuffers
0x0000000141A42AE8 (Unity) QuadTreeNodeRenderer::AddAsRenderNode
0x000000014031F8E1 (Unity) PrepareRenderNodesOnMainThreadDeprecated
0x0000000140327AC9 (Unity) QueuePrepareIntegrateMainThreadObjects
0x0000000140327D6F (Unity) EndRenderQueueExtraction
0x00000001402C2E37 (Unity) CullResults::GetOrCreateSharedRendererScene
0x0000000140BEC2B8 (Unity) Camera::RenderEditorCamera
0x0000000140BEDDBA (Unity) Camera::RenderEditorCamera

Notes:
- THE BUG MIGHT NOT REPRO EVERYTIME: if it doesn't repro, switch between Inspector and Occlusion window, altering Camera's field of view at each step and saving the scene. Also you might try out with adding timeouts between steps (e.g. alter field of view, wait 10 seconds or more, save scene and switch to Occlusion tab and then back etc).
- Reproducible in Unity 2017.2.0b6 and 2017.3.0a2;
- Not reproducible in 2017.1.0f3 and 5.6.1p2.
- Reproducible only Windows 10; not reproducible on OSX 10.12.5;
- Reproducible only with a tree scene, not reproducible in a scene with occluded cubes.